Hehe me again. out of the 3 you picked you might as well remove that sapphire one from the list since its DDR3 which is kind of obsolete by now.. but the 6670 has a higher clock so the 7750 wont be that far ahead or that different from the 6670
Bottom line = best out of those 2 (6670/7750) is the 7750. Even though its on DDR3 i suggest you get it since its newer technology.. well sort of. The 75 series is just a rebrand of the 65 series. 2) That depends on what resolution you intend to play it at.. if you're playing at 720p then you can max out the eye candy in most games with no problem. 3) If your PSU is a generic cheap quality one then i would recommend getting a better one but if its a good brand then you should be just fine
Also i forgot to mention, Would a graphics card be any bigger than the Nvidia Geforce GT 240? As of right now, i don't have a lot of room with the heatsink on the CPU and the graphics card below that. I would say about 7cm at most before it's touching the bottom of the case.