[cdb95z28]

No reason to do this. Your issue had nothing to do with rear caliper sizing. While it is slightly possible you may have overheated the rear brakes if you kept all of the nannies on while tracking, the front brakes still do the grunt work by a large margin. By upgrading to the 6 piston fronts, you are copying what the SS 1LE has for the brake system. Except your SS should have come (in the trunk) with a set of very large plastic brake cooling deflectors that are to be used at the track.

Did you have the SS brake cooling deflectors on when you had issues?

You've also already made a large step in the right direction with using SRF.

The Hawk HP+ pads are a downgrade from your stock 4 piston pad material. The stock pad material (Ferodo) is the same material used on the 6 piston setup on the SS 1LE and the even larger 6 piston set up found on the ZL1. Many SS 1LE and ZL1 owners track with the stock pads and stay within the pad's limitations.

There are many variables that contribute to how hard the brake system is being stressed on track. The 6 pistons will help the track use but it can be noted there are many drivers who successfully use a 4 piston setup. Driver technique, cooling, proper DOT4 fluid, pad material, engine power and track layout play a part.