Note that the 950 Pro can be used without native NVMe support as it has its own boot ROM. Also note that one of the x4 PCIe slots on the E-WS will have a direct link to the CPU, but despite trying I've not been able to find out which one, whereas for the standard WS there was a good diagram in the AT review:
SLI is dead. Using 2-way is mostly pointless these days, so 4 is totally pointless. Btw, After Effects can easily gobble more than 32GB RAM. I built an AE system for someone back in 2013 (3930K @ 4.7, 64GB @ 2133), his test job used 48GB. AE hammers the entire system. FYI I replaced his system recently with a Ryzen 2700X which completely thumped the old oc'd 3930K, with far lower power consumption and basically zero noise (changed the GPUs to 2x 780 Ti, which was cheap). See my updated results:
For CB R20 it was 57% faster than a 3930K @ 4.7.
Infact I'm changing three systems overall, so I'll have a WS to sell soon and two E-WS boards, bunch of 3930Ks and a 3970X. I'm going to keep one WS for future benching and for the moment my editing system will remain an E-WS with a 4960X and 32GB/2400 (waiting for Zen3 4950X for a full platform shift).