My experience has been that my rear brakes do a lot more work than what most people would suspect out on a track - and I've got laser pyrometer data showing that my rear rotors were at least 100 degrees hotter than my fronts immediately after 30-minute sessions to back that up too. I have the STi 4-pots in front and stock RS 1-pots in the rear. After 3 days at Watkins Glen and repeated braking from 130+mph down to 70mph my rear brakes are metal to metal.
I will likely be moving to the STi 2-pot rears in the near future as well to try to at least partly alleviate this heat buildup. I don't think that installing the the RS front brakes on the rear is that great of an idea though - for one thing, the rear brakes are slightly different because they also have to deal with a parking brake mechanism, unless you are comfortable losing that.