Consider what you are doing with your cranking battery throughout the day. Lights, accessories, electronics, livewell pumps and aerators, etc.
Even at 60 amps, your outboard motor will usually not fully charge your cranking battery, especially if you're not making long runs or fishing long periods of time without cranking your big motor. A 10 or 15 amp slow charge overnight will rejuvenate the battery much better than a quick shot of 60 amps for an hour or so. If you can swing the $$ for the 4 bank, then do it. Most chargers these days have much better electrical management systems built in that will shut down each individual bank after a full charge is achieved and manage the batteries to keep them 100% until ready to use.