30 will be fine!
I ran a 42mm offset on my old Cavalier (49mm) and there were no problems. Tramlined a bit more, but then wide wheels will do that anyway.
Alot of the Japanese guys run from what was a 35mm offset car with -10mm rims and such like!

As long as it fits the arch, which will only cause concern if you are jumping up in width a fair bit.