My custom build, quick questions/couple questions/concerns

your psu is underpowered for sli 970's

I seriously doubt your CPU is to blame. The memory, possibly. PNY isn't the greatest or most reliable of memory brands and support for their products can be somewhat hit and miss. I've probably replaced more faulty Adata, PNY and Patriot modules than any other brands I've encountered. Which probably doesn't amount to a hill of beans, it's just what I've seen.

I'd run Memtest on the memory, to at least get an idea if it is for CERTAIN memory related. Memory can pass Memtest testing and still be bad, but if it fails testing it's almost certainly bad.

http://www.memtest.org/

That link is for Memtest86+, I wouldn't use the standard Memtest86 version right now as they seem to have a code issue involving the hammer test that was incorporated into the latest version, so stick with Memtest plus for testing.

The PSU is very good, but definitely underpowered for two 970's whether in SLI or not. Try removing one card and see if the problems persist. If they do, swap it out for the other card and try again. It may be as simple as a faulty card. When you do run two cards, you want a good 750-850w PSU. One of the tier 1 or 2 units here, or another XFX like you have with a higher capacity would be fine:

http://www.tomshardware.co.uk/forum/id-2547993/psu-tier-list.html#15349669



If your only concern is gaming, the i7 isn't going to gain you anything. The 4690k puts up the same numbers, within 1-3fps as the i7, in the majority of titles. There are a handful of titles that are heavily both CPU dependent and highly multi-threaded that do better with an i7 or Xeon E3 chip but those are few and far between, and even then the differences aren't enough to justify purchasing another CPU when you already have a very good Haswell Refresh chip as it is. Unless you have the money to burn, I'd stick with what you have. If you want to chip anyhow, I'd suggest NOT buying an i7, and going with a Xeon E3 1241 v3 as it has the same 3.5Ghz clock as the 4690k, has a 3.9Ghz standard turbo, has no integrated graphics, which you don't need anyhow, has the same eight thread capability and strong single core performance as the i7 and is about 60 bucks cheaper than the i7.

It cannot however be overclocked via multiplier like the K series chips so if overclocking is desired you'll not want to go that route. If you do plan to overclock, you'll definitely want a different cooler regardless of whether you stay with the i5 or move to the i7. The Haswell Refresh chips have a bad habit of increasing heat output exponentially when overclocked and require a VERY good cooler. A single width liquid cooler won't cut it. I recommend the Cooler Master Nepton 240m or one of the 240mm Swiftech coolers, or a custom loop. I'd avoid the Corsair coolers as they underperform and the Link package sucks anyhow.

What does this mean? Your first post indicated you have GTX 970 SLI, so how is dropping down to a 750 and upgrade? Typo? Lapse of reason? What do you ACTUALLY have right now, installed? If you have 2 GTX 970's installed, you DO NOT have enough juice. For one, yes, for two, no.