Hi RickMarx... welcome to the Asylum.
My question(s) center around the fact that I'm looking for a round that offers the best penetration through barriers. Auto glass, steel, etc.
In a conventional sized semi-auto handgun, the .357 Sig chambering might be what you're looking for. Think of it as a slightly slower .357 Mag, or a +P+ 9mm.
If you're not familiar with it, it was designed by Federal at the behest of Sig Sauer in an attempt to produce the ballistics of the 125 gr .357 Mag, in a compact, high capacity auto cartridge. It is based, roughly, on the .40 S&W case necked down to 9mm.
You can buy a .357 Sig chambered handgun and in most cases, typically with little more than a barrel change, shoot .40 S&W... and visa versa.
Another is of course the 10mm Auto... but there are far fewer hi capacity handguns chambered in this round. The Glock 20 and Colt Delta Elite (not hi-cap) are, IMO, the two most well known, with the EAA Witness following not too far behind.