I just wanted to confirm that the Coolermaster 212 evo does fit in the Antec gx500, but if there is any extra space, it's probably not much. I lightly tightened one screw on the mounting arms so it wouldn't fall over, and slid the side on, no movement or extra noise to indicate any extra scraping of heat pipes when installing. This was even with the side window model, and there is no blocking of the side vent fan mount either, at least with the cooler oriented for horizontal air flow to the back of the case. This is with a Asrock z97 Extreme4 motherboard.
Good enough for sub $30 with rebates, but I'd suggest something with a bit more length for the extra space. I suggest running the PSU>CPU cables through the MB cutout at the top left before placing the MB, and pre-attach any 3.5 drive cords before sliding them in as there is little extra room. Also, very little space between the PSU and an ATX board.