What are you tuning to?
I've used all the way up to a .072 for a low B on my guitars. The biggest I've used on a floyded guitar was a .065 bass string, and it worked fine. It sounds different since it's double-wrapped, rather than like a guitar string with a single wind, but other than that, it should work fine, assuming you're not putting some ludicrous tension on the guitar.
Its also worth noting on some exceptionally large strings you may have to either unwind the string to get it to fit through the tuner, or bore out the tuning peg with a drill. I prefer to unwind the string, since you dont have to make any mods. you might have to have the nut filed to accommodate the larger string as well.