more or less anything with 4 cores or more will do. Go for 8 Gb ram ( because it's so cheap ) and something like amd 5770 or nvidia gtx 480 and above. Go for 2gb ram on the Graphics card simply because your textures love it
You can build a really cheap box that will run it well .
( for reference it runs well on a E6600 ( dual core ) with a 8800GTX and 4gb ram . not on max though )