Some history about X99 family

At June 4, 2013, Intel announced the first CPUs based on the Haswell microarchitecture. As the successor to Ivy Bridge, Haswell was built using the 22 nm process and was specifically designed to enhance power efficiency while optimizing the performance of FinFET (non-planar "3D") transistors.
Intel also introduced the first CPUs using the "U" suffix that where the low power processors designed for laptops and ultrabooks.
Some of the CPU features that Haswell introduced where:

• Wide Execution Engine
• AVX2 instructions
• Fully integrated voltage regulator (FIVR)
• New advanced power-saving states, C6 and C7

On the processors including an integrated GPU we can find:

• Hardware graphics support for Direct3D 11.1 and OpenGL 4.3
• 40 execution units (EUs) vs 16 EUs of Ivy Bridge (varies by processor)
• Level 4 cache, dynamically shared between the on-die GPU and CPU
• Support for HEVC hardware decoding

The CPU release was meet with the following socket chipsets:

• LGA 1150 for desktops, and rPGA947 and BGA1364 for the mobile market
• Z97 (performance) and H97 (mainstream) chipsets
• Optional support for Thunderbolt technology and Thunderbolt 2.0
• Shrink of the Platform Controller Hub (PCH), from 65 nm to 32 nm.

In 2014, Intel released a refresh of Haswell, known as "Haswell Refresh." This included the 9-series chipsets and provided minor upgrades to CPU clock speeds, with increases of 100-200 MHz at the same price point. However, by the time the Haswell Refresh launched, the market had already shifted its focus toward the anticipated release of Haswell-E and the X99 chipset.

Intel launched the Broadwell microarchitecture on October 27, 2014, utilizing a new 14 nm process that succeeded the 22 nm process. This process incorporated FinFET multi-gate MOSFET technology. The Broadwell release primarily targeted high-end desktop CPUs, as no low-end CPUs were introduced. Additionally, Intel debuted the "Core M" processor branding, enabling the production of ultra-thin, fan-less laptops.
Intel's CEO at the time, Brian Krzanich, initially claimed that the chips would ship by the end of 2013. However, delays caused by low yields from Intel's 14 nm process postponed the release.
As part of this "tick" release, Broadwell introduced several new instruction set architectures, including:

• Intel ADX instruction set: ADOX and ADCX instructions
• RDSEED instruction set: For generating 16-, 32- or 64-bit random numbers
• PREFETCHW instruction
• Supervisor Mode Access Prevention (SMAP)
• Transactional Synchronization extensions (TSX)

The integrated GPU featured several advancements:

• Hardware support for Direct3D 11.2, OpenGL 4.4 (OpenGL 4.5 on Linux)
• Support for OpenCL 2.0
• VP8 hardware decoding and hybrid encoding support
• Two independent bit stream decoder (BSD) rings to process video commands on GT3 GPUs
• Intel Turbo Boost Max Technology 3.0 on Broadwell-E

The platform controller hub (PCH) is a chipset introducen in 2009 by intel and intended to fix the bottleneck in previous architectures based on north-bridge and south-bridge. The PCH serves as an interface between the CPU and the other peripherals.
Between the extensive I/O support that the PCH provides we can find:

• ACPI Power Management Logic Support, Revision 5.0a
• PCI Express Gen 3
• Integrated Serial ATA Host controller 3.2, supports data transfer rates of up to 6 Gb/s on all ports
• USB 3.2 Gen 2x1 (10 Gb/s) eXtensible Host Controller (xHCI)
• Supports Intel® Rapid Storage Technology (Intel® RST)
• Supports Intel® Active Management Technology (Intel® AMT)
• Supports Intel® Virtualization Technology for Directed I/O (Intel® VT-d)
• Supports Intel® Trusted Execution Technology (Intel® TXT)

Whether this build works for you really comes down to what you need. If you're after top-notch performance or setting up a server for important tasks, it's best to go for newer hardware from reputable brands. But if you're just looking for a budget-friendly workstation and don’t need any fancy BIOS configurations, those X99 motherboards could be a solid choice.
The X99 series was aimed at enthusiasts and high-end users back in the day, and while it might not be considered high-end anymore, the Intel Xeon E5 26XX v4 still packs enough performance to function well as a workstation or server.
However, if you're a gamer or a professional using the latest software, or if you want something that can keep up with future demands, you should definitely focus on newer systems. Modern setups provide better single-thread and multi-thread performance, faster memory speeds, PCIe 4.0/5.0 for quicker GPUs and storage, plus advanced connectivity options. These features are crucial for intense gaming, real-time tasks, or VR applications.

Ultimately, the choice depends on whether cost-effectiveness and adequate performance for legacy tasks outweigh the benefits of cutting-edge technology.

Currently, we can find several options to build a workstation on server using the X99 Family.
Depending on your budget or needs you may prefer a well known and established brand like Supermicro by purchasing a second hand motherboard on ebay and ensuring all the features will be supported with proper documentation, or you may prefer a build combo from aliexpress that will do the job for a fraction of the price.
Both options have their caveats for example not using a brand-new motherboard or trusting an uncertified motherboard without grants that features will be supported.

Here is a list of current brands selling chinese combos including motherboard, X99 CPU and RAM builds and their price:

The prices have been collected from Aliexpress and Ebay and the shipping will be included separately. The prices will vary as well as the shipping but is to have an idea how much the system would cost.
The Aliexpress or Ebay selection will depend on the best listing available.

Without adding the PSU, Case, GPU and other elements of the build and accounting both systems will use the same ECC memory the Ryzen build is 74.15% more expensive than the Xeon system.

Building an X99 system today can still offer significant benefits, particularly for users on a budget or those seeking a capable workstation or server for heavily multiprocessing / parallel tasks. X99 systems, based on Intel's Broadwell-E processors, provide access to high core counts and quad-channel DDR4 memory, which can be advantageous for multi-threaded workloads like video editing, 3D rendering, or virtualization. These systems are generally much cheaper than modern equivalents, as X99 motherboards and CPUs can often be found on the second-hand market for cheap. However, X99 systems lack features like PCIe 4.0 or 5.0 support, higher DDR4/DDR5 memory speeds, and newer connectivity options such as Thunderbolt 4 and Wi-Fi 6E.
This mean a X99 system nowadays is not suited for enthusiasts and professionals who need the highest performance and access to the latest technologies.

On the gaming side X99 systems are not ideal for gaming compared to newer hardware due to several critical performance limitations.
First, their DDR4 RAM speeds are significantly lower, often capped around 2400 MHz, whereas modern platforms support DDR4 speeds exceeding 4000 MHz and DDR5, offering even greater bandwidth and lower latency.
Gaming performance heavily depends on single-thread clock speeds, and X99 processors lag far behind modern CPUs in this area, with base and boost clocks typically peaking below 4 GHz. Modern processors, such as Intel's 13th Gen or AMD's Ryzen 7000 series, achieve much higher clock speeds (5 GHz+), resulting in smoother gameplay and better frame rates, particularly in CPU-bound scenarios.
Additionally, X99 lacks support for PCIe 4.0/5.0, limiting the full potential of newer GPUs and NVMe storage. Features like improved power efficiency, updated connectivity (e.g., Wi-Fi 6E, USB 3.2, and Thunderbolt 4), and optimized gaming architectures on modern CPUs make newer platforms far superior for gaming, ensuring higher frame rates, reduced latency, and a more immersive experience overall.