I was watching an old Galfond video recently where a very similar spot came up. Before facing a river bet, he said "if villain shoves, we can start to think about folding". He also said shoving Ax would be a good play by villain as it gets hero off a chop sometimes. I realised at that point that I'm still a huge fish for not even contemplating folding, unless the overbet is so big relative to the pot that I'd end up losing money to rake in the best case scenario of a chop.

Anyway, Galfonds old videos on YouTube are still worth watching in 2015.