I've now been using an 8707v for just over a week.
Battery life when letting the device choose its network 2G/3G is pretty poor and only appears to last about 26 hours without needing a charge.
I think the reason for this lack of battery life when in 2G/3G network mode is the constant flicking between networks.

Fixed to 2G I'm now on day four of usage which seems inline with my 7290.