If you can get up Ash Street happily with a 39 x 23, I'm happy for you. I can grind up hills that steep in the 23, but it really sucks. It sucks in the 25, but less. There does come a point where mashing the bigger gear is pointless, and a 23 on Ash Street falls into that category. Those other hills you mentioned aren't that steep. Ash Street's a bear. That has to be 17-18%+. Thankfully it's rather short. A 39x 27 would really be better for some grades on some rides around here (the ones like Ash Street like my own hill).