I've been riding on 160mm rotors for a few winter seasons now. They stop me (200lbs), and my loaded commuting rig on steep hills around Seattle.

I recently blew out a rear hub, and relaced my wheel using a Deore LX hub (19.99 on nashbar). I also upgraded the rear brake caliper from Shimano Deore to an Avid BB-5 (shimano was busted and avid was in stock on sale at LBS). I can't begin to explain how much more stopping power the Avid BB-5 has over the deore. I'm sure a BB-7 can only be better.

160mm disc is PLENTY for commuting. Unless you have bald tires or poorly adjusted brakes, you will be able to lock up your wheels anytime you want.