RonCT

No matter what pad you use, your rears will probably last through 2 sets of fronts if not more. I have one event on my 997S set of Yellow / Black (granted, about 6.5 hours at Watkins Glen) and the pads started at about 13mm in thickness and the front Yellows are now about 11 and the rear Blacks about 12.

Acropora

IME blacks are harder on rotors but are more quiet on the street. Don't seem to last as long but bite more quickly at the track. Kinda of a toss up.

MacGT3

Lot's of good advice for pads in this thread.

Now for my advice, whatever Bob Rouleau suggests just do it!!!!