the 48V kit is the better hill climber of the two.
and will range suffer a lot being 48v rather than 36v
Range wise, there is not much difference in battery consumption between the two if you ride the same road at the same speed.
However, it is more tempting to pull away and climb hills faster just because you can with the 48V kit, my guess many people will just do that and battery consumption suffers a little. Still, the Rio comes with 36V 13AH and 36V 17AH, the 48V comes with 48V 12AH. The range of the 48V is in the middle between the two, about 50 miles.