I ran 12v for many years, back when we never had smart converters, and never seen over 13.8 volts, back when we never knew what the importance was of fully charging the batteries, and back when the batteries got boiled dry every summer.
They lasted 3 yrs if we were really lucky.
Then I run 6v for many yrs, on a smart converter w/ equalization etc etc.Batteries lasted much longer, like 9 yrs,
Now I am back to 12v batts in my current RV, w/ charge wizard etc etc.
I'd bet these 12v will last much longer than the ones in yesteryears, we'll see.
But performance wise, AHs are AHs, I never noticed any difference in performance tween 6v or 12v. For me, its AHs per $s !