GPU Wise, Radeon 7770 is a better performer than the 6850 by 3 - 5% & for less $$$ while the older GTX460 is about equal in performance to a 6870 at the same cost as the 7770. As such, here's my suggestion for GPU: eVGA GTX460 Super Clocked
$156.97 after shipping, and is eligible for a $25 mail-in-rebate
IDK, the 7770 is 128-bit memory bus and that 460 is 192-bit, the 6850 is 256-bit FTW (the 7770 and 460s are cheaper for a reason
70 is cheaper because it's a 7 'target', not an 8 'target', the 2nd number of the Radeon card is it's marketplace target, 5=budget, 6=value, 7=mainstream, 8=enthusiast/gamer. While the 3rd number is it's relative performance within it's target series. Yes it has a 128 bit MEMORY bus compared to a 256bit bus on the 6850... however the memory bus width has limited impact on gaming performance provided that there is enough memory to handle the demand
. On a narrower bus, lost performance can be overcome with faster memory speeds. These cards have been benchmarked to death, and these benchmarks using real-world games are readily availalble everywhere. Unless you're gaming on a 30" computer display at native 2560x1600 resolution, the extra bus width on the memory will have minimal impact. More important is the architecture of the graphics core & the cores speed. The difference is enough for the 7770 to overcome the handicapped memory bus in all but the most demanding settings.
The 192bit 460 is the same cost as the 256bit 460 for a reason. nVidia hasn't had to drop the price on either one because they are still a great performance per cost value even though it's a 2 generation old part now.
Early 192bit 460's did show a drop in performance because those were the SE models with 288 shader cores, not current models with 336 cores (same as the original 460) & the current models outperform the 256bit versions because of their large increase in clock speeds. With a 256bit card, you're one of the lucky few if you hit 850MHz core without liquid cooling & a hand picked card like the Galaxy, but with the improved core on the 192bit version, 950MHz is attainable & some have gotten(claimed anyway)
over 1GHz on air. This core speed & resuliting increase in Texture Fill Rate more than makes up for the lost memory bandwidth.
Reference 256bit memory bus 460 = 675MHz core & fill rate of 37.8B/sec - that equates to 0.056B/MHz
Reference 192bit memory bus 460 = 778MHz core & fill rate of 49.8B/sec - that equates to 0.064B/MHz
Even though it's more than just core speed (#TU * core speed),
Core MHz carries a direct correlation to Texture Fill Rate, even as your gaming experience is more than just Texture Fill Rate, though fill rate does carry a direct correlation to frames per second... Basically, a 256bit GTX-460 would need a core speed of around 875 to match the fill rate of a reference design 192bit GTX-460. To match the eVGA Superclocked card fill rate, a 256bit variety would need a core speed of over 1GHz which would require something like LN2 cooling...
A 192bit 460 should handle next years games at smooth playable frame rates & medium to high quality settings at 1920x1200 - the resolution I play at. If I were the OP & building for myself I'd go with the MSI GTX-460 I linked, & upgrade when it became necessary. Which is probably what I'll end up doing for myself anyway, by then the 700 series should be out & hopefully I'll be making a little more money than I am now & be able to step up to a 770.