There's another recent thread in this section where some of the stock voltages are listed. I apologize but I don't have a few moments to add the link, but you should find it okay I think.
If you're getting that many hours out of your regular battery you're doing as well or better than I am. That's why I'm leaving mine at 1.25 lv for now. I hit 30% of moderate usage at 5pm (unplugged since 7am, so 10 hours). I charged it back up to 60% on my commute home and it lasted the rest of the evening with light use. Plus, I did hit over 1700 Quadrant with this setting -- it just took a few tries.
Before that it was in the mid 16's. Enough to eliminate some of the lag.
While running 1.3 using Nav, I seemed to have stuttering issues with the screen, and an occasional reboot. Obviously ymmv since it's different per phone.