How small can you comfortable go for gaming PC?

[HeXen]

You have a video card in there?!?!?

Damn that would be nice, I could mount it to the back of a monitor.

EDIT: I see. didn't know Asus made desktop gaming machines now.

You can put full size cards in it. The secret like any small case is to intake air directly onto the heatsinks and directly outside without any exhaust going inside the case. That's where most small cases screw up.