Thanks for the info...I have a Sig P229 in .40 Short & Weak, which I use for carry and love the gun. I bought a drop-in 357Sig barrel for it and what a fun round. Neat thing is, as you mention, uses the same mags.
Stay safe
The upside to the .40 design is that it fits into most of the already existing 9mm handgun platforms. Browning beefed up the Hi-Power in the .40, and I believe Taurus did as well on their PT-92 Beretta clone platform. The 10mm is longer, and has to use .45 ACP frames.
The .40 is definitely a step up from the 9mm. My logic for choosing the 9mm is cost, which allows for more practicing headshots due to the increase use of vests by “bad guys”. The next handgun I purchase is going to be a dedicated concealed carry weapon, and I am still considering a .357 Sig or .400 Cor-Bon.
I prefer the velocity/energy over the heavy/slow philosophy, but it requires more careful bullet selection to transfer the all of the energy to the target.