Sig makes a wonderful 1911 OP, you won't be disappointed and despite the advice given, I'll advise you not to be concerned with the .45acp chambering. It's a true statement that you most likely won't be able to shoot it well until you become accustomed to the recoil of the round, but the truth of the statement doesn't change if you also own and shoot a .22!? Even in the same 1911 platform or a designated .22 cal 1911 like a GSG (nudge, nudge, wink, wink

) you will still have to expose yourself to the recoil of the .45 acp and learn to manage it. Apples and Pears really.
I own and love .22 pistols. I shoot a lot of it, but the reason I do so is to hone my trigger control, follow up shooting sight picture acquiring, working the firearms controls, magazine changes with chambered rounds, mentally counting rounds discharged, clearing FTF (rimfire crap is great for this training

). Although most of this 'practice' transfers well into a 1911 in .45acp, when I start shooting the .45 it is a different gun, it behaves differently and needs to be practiced with in its own right.
I say buy the Sig OP, along with a 1000 rounds of .45acp in your favorite factory flavor and catch as much of the brass as you can, look to reloading gear. Once you realize how fast a 1000 rounds at $500 (or more) goes by, trust me when I tell you that you will eventually look at a 1911 conversion or a designated 1911 chambered in .22LR.
$500 buys a lot of .22 which equates to a lot more range time, but it's still not .45 acp range time if you know what I mean.
*edit* I forgot to mention that .45 acp is my favorite round to shoot. Even though I appreciate magnums, there is just something about the .45 'thump' that I find satisfying. I recently became reacquainted to the .45 acp through the purchase of a Glock21. Wow is all I can say. The cartridge is great in it's 1911 designed platform, but I have to say that 100 years later, Glock got it right with their model 21. A moment akin to retaking your wedding vows with your partner on a 20th anniversary type moment...well, if you're a red neck that is.
