Rear caliper question

[GregS]

Also as part of the deal I described regarding the 911 rear arms and hubs, I got a set of M calipers (with spacers). I'm trying to decide what to do about the rear brakes, and am unsure of the size of the caliper pistons in the M caliper as opposed to the caliper pistons in the stock 914 caliper. If the M's are bigger, then I'll fight all of those battles. If they don't provide a significant improvement, I'll use the spacers on the 914 calipers and take the easy way to the handbrake. Once again, thanks for your help.