Not sure how to answer the size questions. I haven't carried a wide range of guns to know what I can conceal. For comparison, a Walther PPS M2 basically disappears on me, but my Sig P320 TACOPS grip prints like a third arm. Although I don't think anyone can conceal that beast. LOL
As for why a .45 ACP...I can only say "because I can". I've always admired the caliber, just haven't found the platform yet.
Shield 45 if you want to conceal it, and everyone is a 1911 fan they just have not shoot a good one and been converted yet
For a similar size as the pps m2, the shield .45 would be pretty close. I've been lusting over one myself. Don't know if you shoot Glocks well, but a G30 has a lot of capacity in a somewhat smaller package, although it is big in some areas. Kinda like a short girl with a big butt.
If you want big a p227, CZ 97, FNX, PPQ .45, or M&P might be more your flavor.