Personally, if the expectation is to work 50 hours a week, then the question to ask them is "OK, do you pay 25% more than the average salary for this position?"

Of course, the only reason you'd ask such a question in the interview is that you have already decided you don't want the job. But the response can still be illuminating/entertaining. :)

"Oh wow, you must be burning through a lot of cash paying for all that overtime."

Would probably end the interview right then and there but so worth it to see their reaction.