I've been running a 35 on the stock carrier for 3 years - as mentioned, get a spacer for stock wheel and the Daystar isolators.
I have used my tow hitch receiver as a barrier (flipped) if I felt the spare would catch - it works but sounds like hell but IMO it's saved me from hitting the spare
I've seen guys using a curved hitch bar to do the same thing but haven't found anything like it...
Thanks for all the relays, Lots of good info! Do you guys recommend any particular adapter/spacer? Eventually I would like to get either the Poison Spyder or Or-Fab tire carrier along with different wheels. But for now, I need to use the OEM wheels.