Your right about the Bostons. They would recieve a little more power over the MB's and possibly sound better because of it. The Boston's also have a lower power rating (20-400 as opposed to 60-130). Because of this I think they will sound better because thay are getting power that is in their range; the MB's would be under powered.
I have listened to both (the MB 5.25" in my sig and a pair of Boston 5.25" pros.) Personally I like the MB's because of their higher freq. response....others don't like them because of it. Sound wise it's user's preference, performance wise I think the Boston's would work better in you application.
Hoped this helped...good luck
2006 Jeep Liberty
Adire Audio, Cadence, Clarion, MB Quart
Lv = [(14630000 x R^2) / (Fb^2 x Vb)] - 1.463R
*Vb = vol. in cu"
**R = sq.rt. A / Pi (for square/slot port)