what about amd drivers are they stable as nvidia ..i saw some benchmarks that gts 450 is nearly equal to amd 6770
nvidia's drivers are usually better. nvidia puts a lot of dough in driver dev. but amd isn't far behind. but they do tend to royally screw up from time to time. however, 6750 should have better drivers than 2 gen old gts 450. the 6770 is more efficient. may be the oc gts 450 can get close to a 6770. i know that gts 450's replacement - the 550 ti performs head to head with 5770 (6770 before rebadging) at stock speed. the 450 will have advantages in nvidia-favored games like batman arkham asylum (with physx enabled).
the new 7000 series cards are coming out in q1 next year, with amd's 7970 launching in january... 7670 will most likely launch in march-ish. you could get by using a lower end card/igp and try your luck with the newer cards. imo any one of the new cards should be a good upgrade from gts 450/6750/6770.