Better video card will for sure yield better performance in most games at that resolution.
From most games, better gpu's will give better results than better cpus. Although if you had the money i would try to get at a tri core cpu (like phenom II x3 720). That way the game runs on 2 cores and the third core is running the drivers for the gpu(s) / os background activities.
I recommend a tri core becuase you dont gain very much FPS from tri to quad core cpus but you do gain a decent amount of FPS from dual to tri core cpus on some to most games. http://www.anandtech.com/bench/default.aspx?p=96&p2=83