Possibly you could rent a 40 of any manufacturer at least close in weight, and size to the KAHR. Then you will have a little hands on experience with the recoil of that caliber.
I forgot to mention that I did that. The gun was a .40 all-aluminum S&W DAO, not sure of the model. The kick was rough and the muzzle flip was ridiculous. I just heard that the CM40 had a lower bore axis than other 40's so the flip wasn't as bad.
I'm not afraid of the recoil, (I shoot a .357 GP100 with 125g FMJ's without much of a problem) but if takes too long to regain the site picture, maybe the 9 is best.