ORIGINAL: Diver944
I made the mistake of leaving my brakes as the standard 944 M030 disks and callipers after the power was boosted to 400bhp. A marginally lightened car on R Rated rubber had terminal failure for me. After the repairs I went straight to the 928GTS Big Blacks with new master cylinder and goodridge hoses and they felt absolutely awesome. No soft pedal and plenty of reserve to soak up heat in those larger disks.
I did many, many trackdays at circa 320bhp on Full race slicks with the standard M030 callipers and never had a problem. Make sure you use good track pads like PF97 and run ducting from the bumper vents right to the back of the disk and you'll be fine on a fully lightened car up to 350bhp IMHO
With nearly 500 lb/ft torque its not the best comparison for most 944 turbos! As you say ducting makes all the difference.