Phil, you're paying attention! GM bean-counter engineering at it's best. I've tried many times to get a "straight" answer, and nothing comes back making any sense.
When the Z51 package for the C6 was introduced (2005, I recall), I looked at an early production unit, noting the drilled rotors--I think it was before the parts information had fully updated at dealers--but I couldn't, for the life of me, figure out what the heck was going on. I kept looking at the car because something "wasn't right" and it then hit me that the rotors were reversed--of course I assumed it was an early model, and they had to finish the car, and had not received the correct RH rotors yet. Wrong answer.....
Best I've ever been able to find out is that someone "decided" that testing showed no significant difference in rotor temps side-to-side, so the parts book shows only 2 PN's....1 for front & 1 for rear, used on both sides--and that is the case with each of the brake systems that were offered before ZR1 came along. The previous model (C5) had 4 individual PN's, specific to each corner.
F 325mm directional vane (left & right - separate PN's)
R 305mm directional vane (left & right - separate PN's)
same as C5 above, but pillar vane (non-directional)
F (left & right same PN's)
R (left & right same PN's)
(thru 2009) (drill pattern reversed on RH side)
F 340mm directional vane, drilled (left & right same PN's)
R 330mm directional vane, drilled (left & right same PN's)
(drill patter reversed on RH side) and 2010 Grand Sport with Z51 package
F 355mm, pillar vane, drilled (left & right same PN's)
R 340mm, pillar vane, drilled (left & right same PN's)
As noted, there is a difference--the Z51 rotors are actually directional vane venting, which should be a worst-case situation, trying to flow air out from the rotor center with the vanes acting as a dam, basically.
Turns out that C6 went to pillar-vane style rotors for the standard and Z06 models (rear only, I recall), which don't care about direction of rotation--like a DBA "Kangaroo Paw"
, so any external pattern (slotting and/or drilling) isn't really going to matter as much--for whatever reason the Z51 spec rotors remained directional-vane--front & rear.
Bottom line--the Z51 rotor on the rear is probably large enough that the temp differences won't be a factor unless Scott decides to do some SERIOUS track time with the car.