I've had my Ribelles for almost exactly a year now, and have been super happy with them. I recently encountered a strange quality issue in which the inside lining at the heel completely degenerated on both sides all of the sudden. Photos attached. Scarpa did an excellent job on the CS side - they were actually out of the boots but were able to pull a pair from an in-process order to one of their dealers so I could have my boots before a planned trip later this month. I received the replacement pair today.
Anyway, as far as stiffness goes, it's important to remember that boots can be stiff in any of three ways - the shank can fold like a hot dog, like a hamburger, or it can twist. No lack of love for GoHunt, but it's impossible to communicate all that in a single "stiffness" number.
In my experience, these boots have excellent stiffness in the hot dog and twisting modes, and just a touch of flexibility in the hamburger mode (i.e., there is just a little flex under the ball of your foot when standing on your toes). That said - these are proper mountaineering-stiff boots and toe-pointing up ice with crampons is easily doable.
They are BOMBER waterproof. I've never owned a boot that keeps my feet dry through an all-day session on slushy melting snow, but these do the job just fine.
I did not notice any flex when packing about a bear last fall, ~4 miles with a (measured) 92lb pack over complex terrain in Glacier Peak Wilderness (photo below)