Don't play an awfull lot of cleans myself but I've had a tonal revelation recently which I first tried out on my 7 string electric. I keep the lower three strings on a guage 10 for meatier rhythm tones with the upper 4 on 9's for lead. I'm doing the same now with my 6 strings too but with the upper 3 strings using the 9's and the lower using the 10's.