What gauge strings are best for Drop C and Drop B tunings?

I play guitar and Im really into metal. I like the lower tunings but I never play them because I prefer light gauge strings. I usually play d'addario regular light, .10-46 and I always play in drop D. I want to drop one of my guitars down (Ibanez RG321MH) to drop C and possibly drop B without having to change strings every time I want to go down between C and B. What gauge is good for both?