I currently run Campag Centaur 10 spd , with a compact 50t 34t chain ring and a 11t 25t rear cassette. I don't use the 11t, the smallest I go to is the 12t. I was considering a change of rear cassette, campag do 12t 25t, 13t 26t,13t 29t. My question is due to the loss of the 11 and 12t cogs would I notice a big difference suddenly starting at 13 rather than 12? I want the bigger gear for climbing so should I go for the 13t 26t, or the 13t 29t? Bearing in mind that I run a 50t 34t up front. Your thoughts are appreciated.