From what I heard and read, if you are using the 4 piston brembo's from a 944 turbo all the way around the stock master cylinder works pretty well, if your using the N/A 944 single piston sliding ATE calipers then you will probably need a larger master cylinder because the stock mc just cannot produce the volume that the large single piston needs. As for the BMW reservoir I don't know anything. You can check out the technical section on
www.vdubengineering.com, he has some more info on porsche brakes and on here his name is flat.