If they are the same price then definitely go for the 10250kV motor/ESC combo over the 8750kV motor/ESC combo. You can watch your trigger finger while running indoors with the 10250kV to keep the speeds down, but still be able to unleash pure fury outdoors.
I cannot help with the battery question.. never had either battery or either setup, but I am sure someone here has and can chime in!
Cheers,
Kyle