I am probably going to buy a 9mm 1911, sooner or later, to be a designated training pistol. The more reading I do, of material written by serious shooters, the more I see that a 9mm 1911 may be more susceptible to finickiness regarding magazines, and recoil spring weights. I noticed that Larry Vickers believes that a 9mm 1911 should have a ramped barrel. These anecdotes/opinions indicate, to me, that 9mm is not a best choice, for a street 1911, unless one is willing to pay for a top-tier weapon. (This means a really good one; not necessarily a “boutique” or customized weapon.)
From 1997 to 2002, I owned a .45 ACP Kimber, with its specific role being a training weapon, as it threw malfunctions at me with some level frequency, about one every 400 rounds, more or less. It was one of a pair, both of which started as quite problematic, but I was finally able to get one of them to run well enough to be a duty pistol. (I had a third Kimber, a Stainless Gold Match, which only fed from McCormick Power Mags, while my pair of “classic customs” insisted upon being fed only with Metalform 7-round mags.) I earned a doctorate, in tap-rack. So, yes, I could buy a 9mm 1911, and if it turned out to be a drama queen, it could still have a role.
(I phased-out these Kimbers, in 2002, when I phased-down my 1911 shooting, after I switched to .40 Glocks for police duty, as the then-mandated duty holster made a proper firing grip problematic, interfering with my ability to properly interfere with the 1911 grip safety.)
From a defensive standpoint, independent of the weapon, itself, I am fine with either 9mm or .45 ACP. The technology in controlled-expansion JHP bullets has progressed quite far, since the Eighties, when I started paying attention to such things.
My aging hands appreciate a weapon with less muzzle flip and recoil, but, thus far, I can still tolerate reasonable amounts of .45 ACP, if fired from an all-steel, 5” 1911. A 9mm 1911, also all-steel, would enable me to train more, with a gentler round, which would be more “realistic” than using my .22 LR conversion unit. If it were to run with exemplary reliability, I might carry it. I would like a reliable 9mm Commander-length weapon, as it would clear leather with less articulation of my aging shoulder joint.
If I am without hearing protection, as may occur in a real-world defensive moment, I would rather that my unprotected ears endure .45 ACP than 9mm +P, especially if the environment is indoors, or another type of confined space.