C60 were hella stiff, but they are still made for freestyle big Mtn riding. So less stiff then stiff bindings made for carving or such. Pretty sure this is as stiff as you can get: Freeride 2 Pro EVO bindings
I cant say i have had a pair of these ^ in my hands but i can say that if OP is really looking for a great binding that is super stiff that i can vouch for raidens. The cap strap is awesome, one of the best I've used actually, the airbags are awesome and still responsive and the ratchets are butter.
I have not used the Machines as they were seriously too stiff for me (i weigh 265/270lbs) so i bought the phantoms for great responsiveness and some forgiveness when i fuck up.
IMO for all the features they offer and the comfort you cant go past the machines, the CATEK just don't seem to have the same range of features for a similar price.
my names's Petey and i have gigantic balls