Draco and I were talking to a motorcycle tire guy a little while ago and he said that running 42 front and rear was recommended for most conditions
But if you want best mileage run 50 to 55
This will lower the heat in the tire but will also lower the grip, on the plus side the tire life will greatly improve
Personally I run 42 front and 45 rear and find this is working out great so far
Cheers
Shiney