There are other factors to consider when comparing batteries. I have seen cut-a-ways of the Lifeline products and the difference between the construction of their 12VDC line and their golf cart batteries was telling, with the golf cart series utilizing much heavier lead plates and overall construction.....even better that the venerable '8-D' behemoths.
And speaking of 8'Ds......if you look at the capacities chart on the Lifeline web site: Lifeline Batteries - Marine & RV Deep Cycle Batteries
and look at not only the amp/hour rating, but the 25amp 'minutes of discharge' rate which is particularly useful, you will see a telling difference.
If you compare the 8-D for example, it has a 255 amp/hour rating and 475 minutes of discharge at the 25 amp rate. Now look at the GPL-4CT golf cart battery. It has a 220 amp/hour rating but 492 minutes of discharge at the 25 amp rating...........interesting....more useable discharge time than an 8-D!
Now look at the new GPL-6CT golf cart battery. It has a 300 amp/hour rating but a whopping 690 minutes of discharge at 25 amps.
These are comparing apples to apples by looking at one manufacturers product so there is no brand bias. For me , the choice is clear!