from what i've heard, i have not ridden either one:
The Ep Pro- Basically a super flexy, more noodly and slightly wider version of the hellbent. I'd imagine that it floats a bit better and is like i said more noodly so it will be extremely fun for butters/presses etc. that noddliness has a down side. and it comes into play when it comes to groomers and bigger drops/jumps.
from what ive heard the bents are better at both jumps/drops and groomers just because they aren't as soft as the EP pros. and the Ep pros have more of a rocker therefore you are skiing on less of a ski, they come in a length of 185 but you are probably skiing on more of a 125-135 range.
The Hellbent- Like i said above^ virtually the same as the EP pro but stiffer (barely), less rocker and narrower (122 underfoot EP PRo is 127) I ski the Northwest too, Stevens is my home mountain and next year i am going with the bents as my powder ski. and im going to refer you to my friend "dr.derek" is his name on NS and he rides them and also rides stevens pass he could probably go more in depth but he rides them all the time, even in the park,
so i think that the bents are better all around but the EPs are better in powder