BB7's rock. Anything over 160 is overkill on a street bike unless you're downhill racing on Pike's Peak. My entire fleet is 160 and I live in a hilly area and have never needed anything stronger. Your tires will make a bigger difference than the rotor size. Wider,smoother tires will have a larger contact patch and will allow harder braking.

I would've gone with a Kona Project 2 fork. Can be had disc only and lighter than the Surly.

Are you saying you're running hook rim tires on tubeless rims?