I still dont see a big difference between the 9mm's I have shot and the .40. The .40 I believe is a better round. As far as follow up shots. With a Ruger P89 and the Ruger P94 there was only like a hundredths of a second at most between the follow ups.
As for me I dont want ot have to shoot 16 shots for me to guarantee that they are done. I will take 2 maybe 3 at the most and guarantee the same results.
If it is honestly taking you that long to follow up then something is definitely wrong.