So I sucked it up after reading all of your experiences and put in the extended battery. I got one when VZW did a number on my order that took 5 days to completely assemble a functioning Rezound. I like the high silicone gloss cover for it, btw. More protection than the holster combo.
(can't believe I'm saying this) Y'all are right. I seem to lose the first 10% quickly, but then I'm in a good place. I turned up the brightness to 10% and left all of the other power saving options the same. I think I'm a convert. I'll keep a spare standard one in my toolkit just in case.
It does feel more substantial and fits better in my hand too. Had I not had gotten a free one, though, I probably would have stayed with the standard battery.