Depends - are you happy with your 2 current MF lens lengths, not having a zoom like you're used to, and prepared to pay more for medium format lenses than 35mm ones (I'm generalizing here, but in my searches I've found it to be generally true, esp. the rarer the MF system)?

Don't get me wrong, I like MF and I'm starting to use it more myself, but in general there is a great deal more lens variety at less expense in 35mm than MF - if that's important to you, you might not want to get rid of your F6 just yet.