Updated the OP with what I'm going with...
Received and tore down the rear calipers the other day. They are in pretty dang good shape. I could probably reuse the pistons but decided to go for a full rebuild kit from autofren. f30 335i calipers should get here this week and then I can tear those down. Full rebuild kit for those has also been ordered.
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2011 BMW 128i 6MT M Sport - Alpine White on Terracotta w/ Glacier-Silver trim - Koni Yellows w/ H&R Sport Springs, M3 Control Arms, Euro Intake, BMW Performance Exhaust, 3.73 Diff w/ RacingDiffs LSD Conversion, Black Line Taillights, M Performance Grilles, lots-o-maintenance