I run a 42 x 17 and find it to be a good compromise up and down Berkeley. When you first go fixed, watch out for the bike bucking you like a horse when you forget you can't coast -- you will learn fast. What I learned was how often I would coast for just a second, like when changing my position on the saddle. Also, if you are past your mid-thirties, be sure to actually use those brakes, not your legs, for most of your braking (but you will love the control by just using your legs in slow traffic and at lights).