I weighed my decision heavily on the fact that the OP decided to list which brand of battery was available to him. I chose Lifeline. But all brands of AGM are impossible to get down here. Maybe availabilty is not critical? Or absolutely the last word in capacity vs cubic inches available space?
My choice of Lifeline is based on two things. The battery must not fail - the battery must offer unparalleledd cycle lifespan. Cost was of the least importance. Similar to a cruising sailboat.
I can purchase Deka's best 31 for 197 dollars delivered to my PO box. Now go price a 31 Lifeline. See my point? My second choice would be the Deka. There are other good brands - Odyssey and Fullriver come to mind - but shipping can cost a bundle. The two story 31 Lifeline is my own personal choice because of the same reason as the 31XT. The battery can not fail. I paid through the snot box for that assurance. Maybe others are not in the same position. The OP mentioned need for capacity a.d he mentioned availabilty - I assume for a reason.