Hi,
I know this was posted a while ago and you have no response, so I'm not even sure if you are still interested in applying. But most MFA programs, even RISD and Yale don't really require you to come from a graphic design background. I think I've heard of multiple people who have come from a marketing background and went to design school. The reason why there are no scores you can assess your chances with is that they care about your portfolio and not your grades or scores. There's also an MA Program at MICA if you want do to a 1 year master's before getting an MFA.
My advice is to look at the work of the program - what appeals to you? Apply to those programs whose work you really like, or just go by the rankings. I also recommend looking at where graduates land up after art school and what their job prospects are like. Maybe ask yourself as well - is an art school environment for me or am I more interested in going to a university with a good art program? Since you are currently working as a designer I think you have a good chance!