I like forrest at 4-1. W/o a dog in the fight, I would think its closer to 3-1. My guess is certainly not categorically better than yours.
Still, I think Helmuth -300 is accurate. If they were equal at HU razz I would say -350, but I think Forrest has a moderate edge in experience and skill, and I don't believe Helmuth's supreme skill as an MTTer outweighs Forrest's edges, which are more important even with small starting stacks HU.