6790 is a good mid range card . it can easily handle BF3 at 1080p at high with no AA with playable fps. dont say 720p and low. say that for a 6450 not a 6790.
Not likely. A 6850 can handle BF3 smoothly at 1920x1080 with 'most' settings on high provided that it's accompanied by at least a mid range Nehalem processor. Core 2 Quad processors can handle it but it will run very poorly on a first generation Core 2 Duo.