I just won a brand new set of Shimano XT M775 brakes off ebay. Pre-bled front and rear with everything except rotors and IS adapters for what I think was a good deal at $160 shipped. I need rotors. I want to us a 180 front and 160 rear. Any recommendations. I've decided to stick with 6 bolt. Do I have to use Shimano rotors? I was looking at the XT RT75S rotor. Is there better options from other brands that I should look at?