I currently have Campy Chorus, the cassette is a 12/25. The cassette will soon be replaced. It has been suggested that I go with a 13/26. I live in an area that has lots of short, but steep climbs. I've be told that a 13/26 would be a plus in terms of not having to shift down to the small chainring as often for the climbs. I'm concerned that it may result in lost speed on the flats. Will this make a marked difference? What is the best option? Advice please.