The first handgun that I bought was a Kimber Custom II in .45 ACP. I still have it, and still shoot it a lot. Even underwater.
It's had basically every major and minor part replaced, and it's been completely refinished, because the original finish was simply unsuited to the real world. But that's beside the point. Why did I buy a .45, especially after carrying and being completely satisfied with the performance of my issued 9mm Beretta M9?
Well, that story begins in Iraq, when I was about to redeploy to the United States. I was given an Ambien for the flight back, but ended up not needing it (I had gotten plenty of practice with sleeping in strange and uncomfortable places during my tour).
Once I returned to California, however, I was so excited to be back - and excited to see my family shortly thereafter - that I couldn't sleep that first night and decided to take the Ambien. The next morning, after a solid night's sleep, I boarded a flight for home and spent the weekend with my family before heading back to Pendleton to start checking out of the regiment.
A day later, my dad called me and said that some huge boxes had arrived at my parents' house. Mystified, I asked him to open the boxes. Inside was a Dillon 550B and everything I needed to start reloading .45 ACP, along with a packing slip that put my purchase right in the middle of that Ambien-induced night of sleep. Apparently, I had wandered over to the MWR and ordered everything.
Since I had already bought all of this reloading stuff for .45, I went to a gun store and picked out the .45 that felt the best in my hand and wasn't too expensive. I've since spent at least a grand on replacement parts and refinishing, but hey...
So, there you go. I didn't pick .45 for "knockdown power" or the 1911 because Det One used Kimbers. Or maybe I did pick .45 for that reason, in that Ambien fugue state, but I'll never know for sure.