i ran oem pads in the rear with race pads up front for a couple of seasons of time attack with no problems, however in those days we did the qualy sessions then, only a warm up lap, timed lap and cool down lap, so they needed to get up to temp very quickly, i found the oem rears were great and never had any braking issues.
most of the racecars at TGM run a slightly uprated rear pad, but nothing like the fronts (btcc sized brembos) and dont have problems, when we did uprate the rear calipers on the FD2 for the 24 hr race, the special 'endurance spec' pads wore out at hour 23 so had to change them which is an arse when everything is glowing, the front pads are 27mm thick and easilly last the race. the oem rears and ds pads lasted longer the year before
so , like most things it depends what you are trying to acheive, if you were sprinting, pad choice would be different to vtec challenge, if you are doing regular trackdays and lots of road miles, i would have a second set of discs and pads kept just for track and swap them when i changed to my track tyres, it only takes 5 mins at most to swap the disc if you regularly remove the caliper