Keep in mind processing power, both of g/cards and cores is progressing at it's normal rapid Moores Law pace too.

When I first started 5-boxing (all on one PC) 2 years back I bought about the second best or so g/card I could. Latest cards are putting out nearly triple the performance of it.

I plan on a hardware overhaul for Cata, certainly of the g/card and of anything else required to.