Will definately generate more heat and use more elcetric than a 6 output card. But I've read somewhere that for each 'eyefinity' monitor (the 3rd and 6th) you will need a seperate external power adaptor to plug into the HD58xx and these will be retailing at £100 each .

For WoW purposes only would I be better getting 1 HD5850 and 2 HD4850's, all unlinked or get 3 HD4850's and CrossfireX them?