I got one of these almost a year ago :
http://www.apple.com/macpro/

Obviously, I could justify it for other things than gaming. Anyway, I am now also 5-boxing WoW on it. Really, the confort of 8 physical cores is amazing. With 6 and 8 cores processors in the pipe, this kind of power is going to become much more mainstream in a matter of months. I would really not invest in a full hardware-boxing solution now.