It depends of the games you want to play. Given the benchmarks here
the GTS 450 doesn't look like the best option if you're looking at playing more graphically intense games. The GTX 460 is probably going to be a better option for gaming at 1920x1080 because of how the GTS 450 tends to choke a bit at higher resolutions, especially with AA enabled. Now for something like WOW or even CoD MW:2 you may be able to get away with the GTS 450, but overall I would recommend going for the GTX 460 1GB.