You know, I've done that for years, shooting mostly 9mm and then spending a couple months at the end of year with a .45 1911. I have never established if there was a durable and transferable benefit. I also had a P2000 (I am a 9mm P30 shooter) in .357SIG that I sold almost as fast as I bought it. I do think that I derived something out of those two months as I was more attentive to my grip and sight tracking but I never found that my 9mm performance jumped after I returned back. These days when I shoot my 45s, it is only because I want to shoot them.