But for that extra cost you get four more threads at a higher clock rate, twenty extra PCIE lanes, a 500 MHz higher turbo clock speed, and double the memory bandwidth.
Even with the lesser Intel Core i7-7820X you will get the same thread count but with a higher clock rate, four extra PCIE lanes, still a 500 MHz higher turbo clock speed, and double the memory bandwidth for only $140 more.
Now, of course, the AMD Ryzen Threadripper 1950X comes much closer to the i9-7900X price point.
However, you will sacrifice single core performance to gain twelve more threads at a lower clock rate. But, you will receive twenty more PCIE lanes, over twice as much L3 cache, and the same memory bandwidth as the i9-7900X.
So if your plan is to build a 3D render farm, the Threadripper seems quite appropriate.
Although, if you plan to build a workstation on which to model 3D assets and to perform preview renders--the Intel i9 series seems more apt.