I think the 970 is a pretty sizeable upgrade from the 680.
http://www.techpowerup.com/reviews/G...960_OC/27.html
Looks like about a 50% increase in performance overall. If you look at BF4 it's an increase of 22FPS at 1080p.
I do agree on the 2500K though. Not gonna be much of an upgrade to that. The 4690K is about a 5-10% increase I think. Not really worth the price.
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I have heard reports of some people getting rid of coil whine by stress testing the GPU for an extended amount of time. Sometimes it goes away on it's own after a few months as well. But yeah, it can happen in any card.