Let's not scare the guy. I'm running everything on 'High', and things are pretty smooth. These are my specs:
Intel Core2Quad Q9550 2.8Ghz
8GB RAM @ 1066Hz
ASUS EAH5770 (although due to old card, DXDiag sees it as a 4600 series card and I can't even use DX11 in-game)
Windows 7 Ultimate x64
WD Caviar Black 500GB 7200rpm (almost full, never defragged since 2008 too)
Im running it also on High and no problems so far everything is silky smooth.
Intel Q9550
4GB Ram @ 1066
Asus HD4890 with DX10.1
Win 7 Ultimate x64
WD Caviar Black 1TB 7200rpm