What happens in 6 months if you don't get the bump? Worst case you've improved your experience, got more runs on the board and can apply for another job, closer to the one you want.
I don't know your personal circumstances, but I would personally take the chance, if the new startup job is something you will honestly love doing for 6 months (or more), and you're ok with re-locating across the country for a period of your life. As I said, I'd do it, but I'm not you.