I run 25/78 with the timing nudged up from stock the 30' on my Novak 13.5, and it still runs cool. I go up to a 26/78 when I go back to 30'. I find I can keep up to the 10.5's (
on my track) because the 13.5 is a little more tractable. I lose a little ground down the straight, but make it back elsewhere. I find this website helpful for quick gearing references.
http://www.comeseethis.com/gearing/Default.aspx