If I was to run X0 cranks, chain guide, derailleur, etc. on my DH rig, which brakes should I use? Because I'm pretty sure X0 brakes are only for trail bikes.
X0 does not cut it for DH. I have one that I was running as a spare front on my DH bike and it's for sale. Garbage.
I own a set of 2011 Avid Codes. Very powerful and great modulation. Lightweight (for a full blown 4 piston brake). I do have reliability concerns with them. I have had a piston seize and lever feel can be inconsistant. I have to fuss with them constantly as the brake pads wear.
I took those off and put them in my tool box after awhile. Went with Saint M810 (old Saint). Love them. Even more powerful than the Code's, better feel and although modulation is not quite as good after some getting used to it's a non issue. Stopping power is again excellent. New Saint is even better although I have not tried them I have new XT's that I love. Thats where's my money would be.