I just switched from a G7 to a G700. I have large hands and I think the G7 was a more comfortable mouse. The G7 has a taller arc shape, and it seems slightly longer. My hand just seemed to rest more naturally on the G7 shape, while on the G700 I tend to fall into a claw-grip. The buttons on the G700 are also difficult to push without bracing the mouse with your other fingers. It's an odd mouse. Even worse, there are four of these difficult-to-use buttons right next to each other. They do seem to be getting easier to push as they wear in a little.
Battery life on the G700 is very good. It seems to get several days on a charge, and the cable instantly turns it into a wired mouse - even without a battery installed. The battery is an eneloop AA, so you can buy a few extras and just have a rotation of batteries if desired. The scroll wheel is very very good. The mouse is textured on the sides (like the G9) and smooth on the top, which is nice once you get used to it.
I'm still getting used to it, but I'm torn between the G7 (terrible battery, flaky buttons) and the G700 (less comfortable, stiff buttons). I would love a G7 with a better battery and one more thumb button.