800 is also the spec at 14.5. Drops to 650 at engine off battery voltage. Honestly, id go with the 12W6D4 with the M1000/1. With those 3 ohm specs, you are not getting the return on investment with the 12W7.

If the boat has the OEM installed charger, you are going to be limited to a small Ah house bank, whether wet cell or AGM.

If your plan is to drop anchor and crank the tunes for hours upon hours, drawing down the house bank, an AGM will live longer with repeated deep cycles. For normal cruising and an occasional anchor time, then a wet cell will serve you well.