In reply to Baz P:
No, spring tension is always specific to that particular model. The end result is naturally that it takes tge same amount of force to release the boot from the binding. This all boils down to the binding designs, as they all seem to have slightly different leverage ratios, so naturally the springs need to cater that.
and Yes, the spring tension can decrease over time (especially If you run high settings and do not release the tension during off season). This is exactly the reason that shops will no longer install certain older bindings on the skis, even If they have Nothing wrong with them.