The question obviously depends on a lot of things. Marital status, kids, realty situation, other toys (boats, time shares, etc.), crap like that. So, I was liberal with my vote and went with $100k minimum. Doesn't necessarily have to be single income, either. It just depends on these other factors. For us, I'd like to have an income of about $150k before I felt totally comfortable with a well-appointed M3 given all of my other obligations.