The MK Terrova is a really nice TM, with Ipilot even better. You don't say what method of fishing will be done, but if you spider rig, longline/troll or pull cranks, then the Terrova with IP is the route to go. If you hang out over brush piles, the anchor lock works but not as well as advertised. I have an 04 Tracker PT175, and put a Terrova 55# with IP on in late 2011. The 55 is enough for me and my styles of fishing (longline 99%, pull cranks and shoot docks the rest) and I never run out of juice. I don't stay out 8+ hours like some, usually 4-6hrs is a trip for me. With two batts already, you could go 24v but if your boat is a heavy one, etc., then 24v may be the choice for you. Going from 34# to a 55# would be a vast improvment, I went from 43 to 55 and could tell the difference. The Terrova has the maximizer technology which helps on battery usage, and the variable speed feature helps as well. You may not need two TM batts then.

Think I saw where Cabelas has the 55 Terrova and IP on sale for like $1300 or so in a flyer I got this week. GL