I think it all depends on how ya drive it. A buddy of mine had 35" under his sami with stock axels and breakage never really seemed to be a problem. I only remember him breaking one front axel. He did run Birfield rings in the front of his though.
But, then again, another friend of mine that likes to lean on his a little more has had a few axel issues with his 33's, so he's going back to 31's.