OP a HD 7950 boost represents the best price performance. even at stock speeds this card will be faster than GTX 460 SLI. overclocked it will crush the GTX 460 SLI. remember the HD 7950 is 3 - 6% slower than HD 7970 at the same clocks.
the HD 7950 boost runs at 925 mhz boost speeds. matches GTX 670 at stock. runs at a higher stock voltage of 1.25v. easily overclocks to 1.1 Ghz at stock voltage and can go even higher with voltage tweaking.
" the GeForce GTX 670 is 12% faster than the Radeon HD 7950 and just 2% faster than the 7950 Boost. However the GTX 670 is 27% more expensive than both cards, so whichever way you slice it the Radeon HD 7950 Boost is the better proposition and things just get worse for the GTX 670 as the resolution is increased."
from the review you can see the HD 7950 boost matches GTX 670. Also HD 7970 Ghz (1.05 Ghz) is on average 7% faster at 1080p and 11% faster at 1600p than a GTX 680. HD 7950(1.1 Ghz) matches HD 7970 Ghz.You can clearly see a HD 7970 Ghz is 2x the GTX 560 Ti in most games.
GTX 560 Ti is 30 - 35% faster than a GTX 460.
here is another review of the high end cards with the latest drivers
this review shows a even bigger difference. HD 7970 Ghz is 10 - 20% faster than GTX 680 at 1080p and 1600p. it would require a GTX 680 at 1.25+ Ghz to catch up with a HD 7950(1.1 Ghz).
you can sell your GTX 460 for 100 bucks each. throw in another 100 bucks and get the HD 7950 boost. plus you get 3 very good games for free. go for the sapphire hd 7950 boost. sapphire is one of the best AMD partners.
SAPPHIRE 100352-2L Radeon HD 7950 3GB 384-bit GDDR...