You can only get a PCI-e 3.0 4x M.2 on the X99 boards. You cut the speeds on the M.2 in half or more without the x4 port.
I don't know much about M.2 I just saw that the board I looked up supported it. Still not sure how much difference M.2 would make in a HTPC versus a standard SSD but I can see why that would be a negative.
Okay, what about the i7-5820k then? This is still $349 instead of $1000 and I believe it runs on a X99 board.
Amazon product ASIN B00MMLXIKY