I wouldn't mix brands of pads on the track. Call the guys at Raceshopper.com. they will tell you which pad works best with each other. Great prices also.
The problem most track users have with stock rear pads is that they break down from heat- not so much that the car truly needs so much more brake torque. Adding a competition pad to the rear can help keep the pad from burning up but then the issue becomes too much rear brake torque again. If you elevate the rear pad Cf you may find it necessary to then boost the fronts some also to swing the bias back to somewhat normal.
I've sold many a rear rotor kit (11.75) and as many for this vary reason as for appearances. While we don't 'need' such a large rear disc the added mass helps keep things under control. And when fit with mere street pads still provides a balanced system complimenting the front of the car's big brake kit. *Granted I'd not suggest this without that- merely showing the logic behind such a set up and why.
