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 15" Brahma running off Cadence A7hc, Clarion hu, MB Quart 6.5s and 5.25s running off old school Punch 800a4
146+db @ 38hz with 1200w and a single 15"
Lv = [(14630000 x R^2) / (Fb^2 x Vb)] - 1.463R
*Vb = vol. in cu"
**R = sq.rt. A / Pi (for square/slot port)