school me on 6.5" subs

After re-arranging battery banks and testing out the boat stereo for the first time this year, i quickly found that one of my subwoofers took a crap over the winter which is causing me to re-evaluate my entire sub game.

I have/had two Boston 10" G3 subs with a 1200.1 class D amp.

I have a small amount of space for subs in a Calabria with under floor hard tanks and a short freeboard.

Two questions:
1. has anyone had any experience with 6.5" subwoofers JL/Wet Sounds? Pros/cons?
2. with my limited space I'm thinking of going with one of the following:
a) four 6.5" subs
b) three 8" subs
c) two 10" subs

Open to suggestions.

Thanks!