I don't even see this as a caliber debate...
The OP is talking about disposing of a Kahr for a CZ...and NOBODY finds fault with this??
That's like disposing of a Corvette to get a Chevy Spark.
Keep the Kahr, you'll be sorry if you don't.
Buy the CZ outright.
FBI just went back to 9mm, guess what ammo will be in stock during another ammo crunch?? 40 Short & Wimpy
Now, to the caliber debate.
Back around '95, we were shown a dashcam vid of an officer-involved shooting.
A Crack'd-out 300-lb man was engauging PD from his front porch & had a Glock with a 15-rd mag...
the five officers, during the firefight, hit the man 17 times, including two head shots with 9mm...
yet the man continued to fire back until his ammo was expended, then threw his gun at the cops,
drew a large knife, and charged at the officers...
whereupon an old Sgt pulled his duty shotgun out & fired two quick head shots at Point Blank range on the charging man,
putting an end to the miscreant.
All On Dashcam.
What was learned from that??
Prefer a heck of a lot more than 9mm when dealing with druggies. Especially a BIG one.
Yeah, seen a .22lr drop a drunk in a parking lot (Boomerzzz O.I.S. in Pensacola, FL), but it sure ain't optimal.
.40 Short & Wimpy?? Might as well if you aren't going to use 10mm or .45acp
Shot Placement is Very Critical, even a moderate head shot can have no real effect, better hit CNS.
If using mouse calibers, Shot Placement, Shot Placement, Shot Placement.
And finally, MUST have a hand-to-hand plan & skills if the shooting doesn't work...
and you better be really good at it. Krav Maga or Aikido is suggested.
But any martial art, practiced regularly, is better than no hand-to-hand training at all.
Even old pharts with nothing but Tai Chi can whoop up on an untrained perp.
Or, be like this gal after taking a 9mm to the arm...