Trying to decide on which one to get. Main games I play are GTA 4 and Warhead. My res is only 1680x1050. I love being able to use AA on games and that is what has me looking at the 1792mb. Will the 448bus be able to use that 1792mb? Should I just buy the 896mb? Any help is appreciated.
Also, I don't want to upgrade for at least a year and a half.
Yes, but only to a point.
At your resolution, even 512Mb is enough.
You only start using more than 512Mb while running 1920x1200 or higher and usually with AA and all the other eye candy turned all the way up.
While 1792Mb may help you get some extra performance when gaming at 2560x1600 or higher, it will do little/nothing for you at a lower resolution.
The GTX 275 would have easily handled 1GB though...
But I dont understand why they have such uncommon RAM capacity??? (768 for the 8800GTX, and this 896 for GTX260, 275)...Could any one care to explain...
The amount of memory in Mb's is always a multiple of the GPUs Memory Bus Bandwidth.
The GTX 260/260 core 216/275 all have a 448 bit bus and, as such, it can use any amount of RAM in multiples of 448Mb.
The 8800GTX/Ultra has a 384 bit bus so it supports memory in multiples of 384Mb where as ATIs current top end cards all have a 256 bit bus and support memory in multiples of 256Mb.
OP, GTA4 is a very poorly coded console port.
Even so, when tested at 2560x1600 with identical settings, there was a negligible performance difference.
Looking at the Farcry 2 and Empire: Total War results, also at 2560x1600, the performance difference is also negligible.
The only real improvement the extra 1Gb had was enabling 8x AA in Empire: Total War.
As you are gaming at 1680x1050 and I doubt you are upgrading to a 30"+ ultra high res monitor any time soon, the extra RAM will do nothing for you other than drain your bank account faster.
In GTV4 if you have view distance and detail distance to 30% or 100% there is no visual difference so is mach better to have those two to 30% and you will get 60fps+. is not like crysis that form high setting to very high setting there is a big visual differences.