Brodotron :
Im thinking my GPU's are limited by the fact that I've only got 2gb vram.
For now its fine for 1080p, but soon its not going to be. :/
Not so much.... alienbabletech did a study that showed no discernable difference in performance between 2Gb and 4Gb 770s in like 40 games. Guru3d did it with the 960 with similar results
http://www.guru3d.com/articles-pages/gigabyte-geforce-gtx-960-g1-gaming-4gb-review,12.html
https://www.pugetsystems.com/labs/articles/Video-Card-Performance-2GB-vs-4GB-Memory-154/
So while those test prove w/o a doubt that everyone screaming for 4GB back when the 7xx series was current was definitely barking up the wrong tree. The Guru3D shows that it is till very true today except that some of 2015's games like SoM, Witcher 3 etc have now broken that barrier. However 4 GB is more than sufficient for any resolution up to 4GB....even when utilities report that the system allocated more than 4 GB, this is wrong, ... if ya wanna know why, it is explained in detail here which should put thisissue to bed once and for all:
http://www.extremetech.com/gaming/213069-is-4gb-of-vram-enough-amds-fury-x-faces-off-with-nvidias-gtx-980-ti-titan-x
If ya sold the 760's for $75 each, that would put you about half way to a 970 which is the current "best bang for the buck" available at this point in time w/ more than satisfactory performance at 1080p and 1440p.
http://www.techpowerup.com/reviews/Powercolor/R9_390_PCS_Plus/30.html
The 970 tops the 390 outta the box, at 1080p and while it's about 1% behind at 1440p "outta the box", from your post it's obvious that you are not averse to overclocking.
The390 and 390x have limited overclocking headroom and overclock only about 7% ... with the 970 averaging about 17% OC's, it 's able to pass the 390 and 390x at both 1080p and 1440p when all cards are OC'd. Your HX750 will be more than enough PSU for two 970's in SLI... for the 390 / 390x you'll want 850 for CF.