[Gordon (NZ)]

Say the E key is lifted. I could be wrong but I rather doubt that any player's finger leaves that key before the key fully opens.

Therefore the limiting factor is the speed of a finger.

Curve a hand and place all fingertips on a desk top. How fast can you move a single finger up and down. It's not very fast. I think springs probably move keys considerably faster. Maybe marginal for the low, heavy keys of a bari, with their large angular momentum. But then do you expect to hear an ultra fast, low trill on a bari?

 

[Gordon (NZ)]

Fingers seem designed to tap down a lot better than they lift up. To do with the curved design and linkage to the forearm muscles that operate them.
So do fingers just prefer a bit of spring tension to help them lift?

Balance in the way the keys are mounted is a very significant factor. Especially with vintage saxes, some springs have to lift the weight of a key a lot more than just rotate it around its pivot. That means that unless the spring is a lot more powerful, it lifts the key sluggishly. If the spring is a lot more powerful, the little finger in particular has difficulty operating it, especially if there is very little leverage where the touch piece is, as is common on non-Selmer vintage instruments. Selmer had an excellent design engineer around Mark VI days, and that set the pattern for most modern horns.