I'd go ahead and put the same race pads in the rear of the car as you're using in the front. (in fact, if there's a level HIGHER, I'd consider it for the rear)
Why?
If you upgrade the front pads and go stock in the rear, your front pads are going to grab harder and sooner than the rear pads, meaning you'll be doing more braking with the front than the rear, thus putting MORE load on already overworked front brakes. Put good pads in the rear so that they can do their share of the braking!
Why put better pads in the rear than the front? Because most cars are factory set up with a front brake bias. Same reason they design cars to understeer, it's safer for the front brakes to lock up before the rears. The budget-racer's method of adjusting brake bias is simply to use different compounds front and rear.
I'm probably giving away somebody's secrets here, huh?
Lemons South 2008 - Fail, Lemons South Spring 2009 - Fail, Lemons Detroit(ish) 2008 - Fail, Lemons South Fall 2009 - Fail, Lamest Day 2009 - Fail, Miami 2010 (Chump) - 2nd!, Sebring 2010 (Chump) - Fail, Cuba 2010 - Crew Chief, Roebling 2011 (Chump) - 8th!, Sebring 2011(Chump) - 19th!