Out of those two I would recomend the Hellbent over the EP pro, One of my friends road EP's all last year (he got something like 100 powder days) and wishes he had gotten the Hellbents, their stiffer which makes them just that much more stable.
I would also widen your range to include the armada ARG, and the Moment Donor Party, and Bibby pro. The Bibby is stiffer, which really helps on stabalizing the ski in more variable snow conditions. The nice thing with rocker is that you don't need such a soft ski for powder as you normally would.