Vram does not mean faster - this is a misconception that is confusing people
More Vram = Higher quality @ higher Resolutions
GPU, VRam Speed, Bus Speed, Firmware Drivers, Display
A 1 Gig 750Mhz GPU with ddr5 Vram will out preform a 4 gig 600 Mhz with ddr3 VRam
Being ignorant of this is your loss.
A newer Card with updated firmware may be more user friendly with newer games than older technology and also provide more features. not necessarily more speed just because is has double the Vram.
I have not looked directly at the specs of these 2 cards you have listed. so wont advise of the better card for you... you can work that out... this post is mainly for the ignorant Vrammers. ;P