I'm looking into a workstation build and I want lots of PCIE lanes to feed 4 GPU's for high performance computing. I've considered the ASUS WS X299 SAGE and a 16-18-core Core I9 and the WS X99 SAGE with an E52600v4 series with similar specs. 
 
Then I priced out options with the WS C621 SAGE for the Xeon scalable processors. Dual socket - same price as either above.
 
Here's what's interesting and I wonder what I'm missing - but 2x Xeon Silver 4114 provide a total of 20 cores and 40 threads - for less money. They go for about $750 each, $1500 for a pair of them. The clocks are slower on the Xeon, but there's 20c/40t for less money than a 7980XE (18c/36t) and I can use the cores more than the raw clock. Lots more RAM capacity too, and a huge upgrade path if I should somehow find an extra $20k to spend on Xeon Platinums. Compared to the Broadwell Xeons (E526xx-V4), the 2x Xeon silvers are about half as much for the same core count. 
 
I wish Intel's Xeon naming and marketing had any clarity to it. It took a while to wade into all the various levels and colors and number combinations to arrive at this. 
 
The rest of the build, more or less the same ballpark costs. So what am I missing?