Sorry to say but the SFF Dell Optiplex 790 has a 35W GPU Limit on the Motherboard. The best GPU You will get in this system is a 1030. But around the same price you can buy the MT Version which has no GPU Limit and can house some pretty overkill parts. Also you will have issues finding a PSU That fits in the SFF Variants if you ever planned to upgrade it. I'd just get the MT Version or the Dell Optiplex 3010 as they are found cheaper than the 790 for some reason and they have Ivy bridge CPU's not Sandy Bridge.
Thank me later