wandering_logic

The main things to look for are a sufficient number of PCI express lanes, a high "turbo" clock speed, and sufficient memory capacity and bandwidth. The E5-2698 v4s used in the DGX-1 have 40 PCI express lanes, a 3.6 GHz turbo clock, and 76.8 GB/s memory bandwidth. So does the Core i7-6900K. (The Core i7-6900K has a max turbo clock of 4 GHz, but fewer cores, and smaller total DRAM capacity than the E5-2698v4 (128GB vs 1536GB).)

Bottle necked on the CPU, yes, but probably only on a single (or a small number) of threads on the CPU. Xeon Phi will give you lots of slow threads. For the CPU you'd be better off getting a low-core-count processor with the best clock rate you can find/afford. The gamer-oriented i7 extremes are usually good.