[ciaran]

OK there's about a 20% chance villain wins this hand if he's freerolling the flush and Hero only splits otherwise, and a slightly higher chance that he fills up on the river if he has a set, though in that case Hero has a huge advantage the other 70-odd percent of the time.

I suppose depending on the payout structure you could make a case for folding (I'm not going to do the math, but I can fathom the possibility), but that would only be the case if you absolutely knew he was free-rolling with Ax clubs. I doubt there has to be much chance that this is a set/two pair/ass-end of the straight to make the potential for doubling up rapidly outweigh that possibility though.