As an owner of an 9600GT, it is still a capable card at an affordable price. It's a bit old I suppose since it came out in 2008, but at that time it was considered an above average mainstream gaming card.
The 9600GT very close to the newer GT 240 in terms of performance. The 9600GT is a DX10 card while the GT 240 is a DX11 if I am not mistaken. The GT 240 is considered a value segment video card. See following review for benchmarks of the two cards and some other cards as well.http://www.xbitlabs.com/articles/video/display/gf-gt240-1gb.html
In terms of resolution, you should look at 1280 x 1024 since it is close your monitor's resolution. Your monitor's resolution is actually about 20% less than the lowest resolution they tested. Therefore, you should expect better results than the benchmarks in the review if you were to use the same graphics settings and assuming you are using the same CPU (Core i7-975 Extreme Edition) which you are not.