Intel x99 memory and cpu inquiry...

Even getting dual channel (2 module) kits to 4ghz and beyond is hard in the best of circumstances. The X99X Killer is not a high end X99 board, if you want to even try to get 4ghz on the RAM you should be looking at the X99 OC formula. Even on that there is no guarantee you will succeed but if any board can do it, it's the OC Formula. 

Newer boards like the X299 series will probably start seeing 3800 and beyond speeds achieved more readily moving forward. Most 4000+ kits are still just ridiculously high binned RAM (hence the cost) running at near dangerous voltages and loose timings. My 3600 kit for example can only manage ~3800 at it's rated voltage and it is a reasonably high binned kit. Joining the 4000+ RAM club is not easy yet and also not at all worth the cost, not for the amount timings need to be relaxed to achieve it. In most situations a decent 3200, low latency kit will perform almost identically.  

I hope this helps. 

Got an old Xeon cpu to flash BIOS given motherboard didn't recognize 6950x. Upgraded to version 3.10 and successfully boots 6950x. Made some modifications to my list on SSD's and some hardware. Getting closer. Last items I plan on buying are RAM modules, plan on G.Skill F4-4000C18D-16GTZ kits...