A follow-up report on battery life with the extended battery: I charged it to 100% as of about 10:30 p.m. Tuesday. It is now 8:30 a.m. Friday, 58 hours later, and the charge stands at 12%, low enough to get warnings from the phone to charge it, which I'm going to do.
Obviously this includes two overnights when I was not using the phone at all. I don't do any game playing or very much music streaming (and no video streaming during this particular time period). OTOH, I do leave the Bluetooth and GPS turned on all the time, even overnight, just to avoid having to remember turning them on when I go out. I do spend a fair amount of time on Wikipedia and other Web browsing, a newspaper-reading app, and Google maps. The phone requested to go into power-saving mode when the battery reached 20% earlier this morning, but I declined that for the sake of the testing.
Of course everyone's phone use and experience will be different, but 58 hours to go from 100% to 12% seems pretty good to me.