I've had this Z87X-OC board for about 3 months now and it has run with no freezes up until about a month ago. I began having lockups at least 3-4 times a day, maybe more, sometimes seemingly related to disk copies over USB2, other times seemingly caused by a rapid mouse movement. Nothing specific exactly.
I'm running the 4790 with 32gb Crucial Ballistic Sport ram.
Keeping cpu clock at stock, I bumped the ram voltage up to 1.6v and ran the memtest86 overnight for about 14 hours with zero errors. So at least that would seem to exonerate the memory, though I guess you could say that wasn't thorough enough.
Finally today, I took two steps... first, updated bios to F9a beta, then, noticing some interesting new settings in there, I went for the 40% "cpu performance enhancement" or whatever they call it.
Long and short, I've hammered this thing all day and had not one lockup. It's back to 1.5v on ram, 1600mhz, and reliably running at 4.4ghz with stock cooling. I have no idea what temp CPU runs at as I can't find a temp monitor that reads it but the CPU fan just idles along, unless I jack it up with prime95 or something else. BTW, if anyone can tell me what program will provide temp monitor on this board I'd love to see it. There has to be something, I'd think.
So, I'm thinking possibly the bios update may have fixed this particular board, and the fact that I can bump the CPU up with no ill effect whatsoever tells me we may be completely stable at this point. I'll update after we get to the first oil change.