that is an interesting question, The Hellbents are reverse camber and the Ep's are rockered in more tail tip from what i know. The Hellbents as you know are the bigger ski at 132 mm underfoot vs. the EP's 127 mm underfoot. The Hellbent skis a little more a water ski but they absolutely dominate the Powder and they are made can drop big cliffs if thats your thing but they are at home with the back country freestyle, big spins and landing switch, a big percentage of the top backcountry freestyle kings ski the hellbent, Pep F, Andy Mahre, Charley Ager, and the legendary Sean Pettit. All those guys are at the top of their games and they ski the Hellbent and they all land switch the majority of the time.
The Ep pro is a great ski though, as i said before its the smaller of the two, but they still ski like water skis because of the early rise tip and tail, but because of that they will be easier to manage on the hard pack. They like the Hb's are made to stomp big switch hits in the Backcountry The Ep's are a little easier to manuver in the narrow steeps because of they are smaller underfoot so it does not take as much to muscle them. Both skis are good in the slush and corn days, fun to butter with and smear and just have all around fun. So remember though that both of these skis are made in the same factory, and that yes they are different companys but they along with Volkl are all owned by the same company (jarden inc), so they operate as different companys but they share technology and construction etc. So in my opinion the Hellbents are the better skis, and next years are really fun skis to ski, (skied them last week) in chest deep pow. so hope this helped