As a followup to my original post, I emailed CCI about 22 mag loads, and rec'd this reply:
"Check out our new Speer 22 WMR rimfire load designed for 'short barrels' on Speer Ammo - Home Part # 954 This new load was developed specifically for your application. Linda"

This load and the Hornday Critical Defense 22 mag gives us two excellent choices for carry ammo. I have not been able to locate either round to try however. I plan to run some chono tests as soon as I can come across some of the "short barrel" loads.
In past tests out of a 6" M48, I averaged the following:
Fiocchi 40 JHP 1557fps
Super X 40 JHP 1421
CCI 40JHP 1489
The same day I also tested 22lr out of a M17 6", with the following averages:
Rem 37gr HP 1070fps
Fed 37 HP 1059fps
Super X 40 gr 1027fps
CCI Velocitor 40gr 1110fps
Rem Yellow Jacket 33gr 1229fps