Replaced my 42t chain ring with a 45t Rocket Ring that I picked up from Sheldon. Kept the 16t cog on the back. Even though this change adds only about 5 gear inches (75.9 up from 70.9--w/ 170 cranks and 27in. wheels), the difference on the road is phenomenal. My biggest concerns about going bigger were being able to get a jump on traffic from a standstill, and the two moderate hills I encounter on my ride home from work. So far, no worries on both fronts...and the ability to build speed, without spinning like a phreak, just rules. I was twenty minutes late to work this morning, because I couldn't bring myself to ride my desk all day before doing some time trial work down M street. What a great way to start the day.