3S Pro has first generation Curv and the Ultrasonic has second generation Curv (Carbon Curv). Carbon Curv is stiffer. The tongue on the Ultrasonic is much better than what was on the 2S Pro. Not as stiff and flexes nicely. The tongue on the 3S Pro is somewhat close to that of a traditional Supreme felt and IMO makes the 3S Pro close to the feel of what the 1S was.
How long a skate lasts depends on several factors such as skaters weight, how often they skate, and how well they take care of their skates. My 2 year old 2S Pros were structurally just as stiff after 2 years of use skating 5 times/week. Disclaimer: I remove the footbeds and dry them on a boot dryer after every skate.