I did some playing with rails, and it seems there is a diminishing return on powered rails up a hill. You can't just power it up a hill, you need the cart to be going full speed to make it up any sort of distance. To make it up your hill @
GasBandit I needed 13 powered rails before the start of the hill to have enough momentum make it.
Corners aren't too bad, unless you have a turn at the bottom of a hill. An unpowered powered rail can slow you down, but that pretty much makes it a one way track. Maybe a detector rail could fix that. You still need a good long stretch of powered rail to get you up a hill, so having a turn that close to a hill will be an issue no matter what.
It still seems like a change meant to do nothing but make the game more complicated, which is not the best for a game like this.