I'd advise heavier strings (11's, like Ratrod says, are a good place to start) and then adjust your action to suit. I'm only down a half on my main guitar and another is tuned the same, but the 6th is dropped to C#/Db using EB Hybrid's (9-46) set. Works for me (and with minimal tweaking, usually intonation only).
If you're chopping and changing your tunings, it would be wise to set one guitar for one tuning, rather than use one for loads of different tuning's. If you do that regularly without checking your neck, then it could well lead to problems. If you have, say 2 tunings, then I'd recommend having 2 guitars (not always possible I know!), if that's not possible, then don't change the tuning too often, and always check your neck when you do change tuning. Just be careful.
Don't forget though, that in their heyday, Tony Iommi used C# tuning using 8's!