Caliber

Good point.  Bigger is better, yes, sometimes.  And certainly correct when written, in the 19th C.  As .30 cal was underpowered and thus undesirable, then.  But when velocities went up that changed everything. 

If it was possible to up pistol caliber velocities by a factor of 2+, then switching from .45 to .38 or even .25 would make a lotta sense. As it is... With your pistol caliber selection, pretend you are firing a rifle but restricted to black powder as a propellant as you'd have been 140 years ago.   Of course you go with Big and Slow when your only alternative is Small and Slow...