In a boat, on water and without obstructions (Like trees), you want speed and handling. Two 6-Cell packs just won't cut it. Go as big as you can in the beginning and you will be MUCH happier.

I highly recommend the IB3800 Cells. I have a super brain 977 and do charge my twin 8-cell IB3800 packs (Self made packs). The combo works great (977 and 2 8-cell IB3800 Packs). At some point, you may want an extra prop if you plan to launch/retrieve from very shallow banks (If you don't step in the water). The xtreme comes with a carbonfiber prop, so it is WAY better than stock. The plastic stock & carbon fiber prop are fairly easy to nick if going through mud with any shells or rocks, so buy one if you want one. They can get chewed up, but I have not ever shattered one.

I bought the Aquajet 775 last fall (After selling my Nitro Kyosho Jetstream 1000) and in the spring will have added all of the Xtreme upgrades anyway (If I don't go brushless). Steven, the owner over at Offshore Electrics frequents these forums and is a great resource on the boats in general. If you email him, he always responds.

P.S. The Superbrain 977 can operate from 120v house AND 12v auto, so you can charge at home or on the go (And has Lipo ability).