Sorry just to add to what I just said the difference between a G840 and the i3 2100 is on average less than 5% FPS difference while the diference between a 4670 and a 5770/6770 would be more than double and the jump to a 6850 from a 5770/6770 is another 20% ish see http://www.anandtech.com/bench/Product/296?vs=291&i=188...
^With the HD 4670 or HD 6750.
If it's the HD 4670, at 1280X1024, it won't perform at maxed out settings but well at the res you stated.
The same goes for the HD 6750. It will perform better at even higher resolutions. So you're good.