Brake pad question 81 - up with triple disc brakes

I have a 82 KZ1000 CSR. The factory parts catalog shows different brake pad part numbers for the front and rear. Front: 43082-1007. Rear: 43082-1025. These pads also fit a number of different models. The pads are physically the same size and are inter-changeable front to rear. The calipers are the same front and rear. When you buy after market pads both front and rear are the same part number. Does anybody know what the difference is in the factory pads?
I assume it is the compound of the friction material.
The reason I'm asking is that I installed some after market sintered bronze pads ( store.sixity.com/Items/004000361?sck=129...s%20Sintered%20F%2bR )that are all the same front and rear.
The rear brake seems to be getting quite hot after a spirited ride down hill through the twisties. It even turned a bit dark. Before you ask: the whole rear system is completely re-freshed with caliber kit, master kit, braided hose and adjusted properly as per the factory service manual. The pivot points are clean and greased and the calipers were assembled with Sylglide on the back of the pads and the slider shafts. I even installed new rubber bushings on the shafts.
I'm thinking of trying a set of factory rear pads, or maybe EBC pads. BTW the brakes stop perfectly fine and the fronts aren't getting as hot or bluing like the rear one. Maybe its just normal. Anybody seen this? Thanks!

Is it possible that you could be resting your foot on the rear brake pedal? It sounds like your rear brake is dragging ever so slightly, but with all new parts it would seem that the caliper "should" be functioning correctly. Can you get the rear wheel off the ground to see if the brakes drag at all?

Might help to increase gap between rear brake push rod and m/c piston.
Especially where rear brake seems to function okay when cold, but then begins heating enough to cause dragging, which may ultimately progress to lock-up with a blazing hot disc.

Good Fortune!