A new 115 can mow in reverse and cut low. I just bought a 135 myself, I prefer the twin and hydrostatic transmission, much easier to use and worth the money IMO.
Uneven is no problem, my 135 has been floating across the lawn and mine is very uneven in places, if you get to a spot that's to uneven it will just shave it to the dirt and keep going.
FYI my 135 cuts low better then my LT166 does, more power and a better deck for cutting low.