I own the Cypress. I purchased it overfilled through Hermit's Hut. My son owns the Bison. Also purchased overfilled through Hermit's Hut.
What has been said is spot on. "The Bison is designed the keep you warm at -40 by using extensive amounts of design with minimal amounts of down."
Whereas, "The Cypress is designed to keep you warm at -30 by using a minimal amount of design with massive amounts of down."
We are both roughly 6', 160lbs.
I fill my Cypress with Nalgenes, electronics and down blankets which improves its efficiency.
These are the 2 biggest, baddest bags on the planet, but when it's -30, having one is just part of the equation of a successful night's rest.
