I recently built a Linux PC because I decided I wanted to try and play games on Linux with the increase in the number of available games. In addition, Steam is available on Linux and I wanted to try Crossover, the software that uses Wine to run apps and play games on the Mac and Linux, on a Linux box since I have only previously tested and used it on the Mac. I used a Dell Optiplex 780 SFF and had no troubles loading Fedora Core 19. I went with the x64 load and put 16 GB of RAM in it because that is the most the PC could hold. With video cards your options are limited in a SFF PC, so I started with an Nvidia GT 620 video card but later moved to an AMD 7750 after I found this awesome card in a LP configuration on Amazon here. Neither video card had any problems in Linux.
I found that Crossover actually works much better on Linux than Mac OS. More of the games I test with Crossover work with Linux. And Linux plays games much faster. I loaded Unity of Command on Linux, and although I could not get the sound to work, it works much faster between turns.
So I am enjoying my gaming and playing around with Linux. The SFF PC is small but works great and this gives me an excuse to mess around more with Linux. Not as user friendly as Windows or Mac, but more control and less baggage for you. Give Linux a shot if you haven’t yet.