Re: gel, AGM, Lead acid
Don't be lured by any sale price. As Rick said, AGMs need to be fully charged frequently and they often don't last as long as you'd think they should in cruising boat applications.
Further, unless you have an advanced charging system, you can't really take advantage of the "advantages" of AGMs in terms of charge acceptance. AGMs can easily take their AH rating in charge current when they're down by 50% or so (that would be >400 amps charging current in your case).
Best bang for the buck is still the flooded battery. These, especially golf cart batteries, tend to take more abuse and last longer (more cycles) than AGMs. However they, too, need to be kept as fully charged as possible to avoid the dreaded sulfation of the plates, which reduces battery capacity.