Actually, ACP stands for Automatic 'Colt' Pistol, of which there are several calibers from .25, .32, &.380 (9mm K) to .45ACP.
Especially if the pricetag is no object, the .45ACP H-K USP is about your best choice.
Rather than deal with amateur opinions, I have found that the professional evaluators, both commercial and independent, have given a slight edge to the H-K pistols, from tests run by evaluators from such sources as Guns & Ammo, American Handgunner, and Gun Tests magazines.
In such tests, the H-K USP models had fewer malfunctions and NO (0) failures when tested against, not only the Sig-Sauer, but Beretta, Springfield, and S&W models, as well.
I've run nearly 5,000 rounds through my H-K USP .45ACP, including Hydra-Shok, Cor-Bon, and several equivilent custom handloads, with 0 stoppages EVER, and it's tolerances haven't measureably changed since I first aquired it.
Know also that I carry my USP .45 in 'Condition One' (c0cked & locked) with a round chambered, just as safely as one can with the 1911.
The only negative factors I've dealt with carrying the USP, inherrent in the SOCOM, as well, is it's larger size, but I'm a larger guy and LIKE the more impressive size, and the limited availability of carry systems, but I carry concealed in my own unorthodox manner, anyway.
Legal Arizona CWP armed citizen,
w/ H-K USP .45ACP
Life Member: N.R.A. & G.O.A.
Former U.S. Marine
4x Rifle & 2x Pistol Expert:U.S.M.C.
Firearms owner,including Luger P-08, H-K, Glock, S&W, Colt, & Walther pistols.
35+ years reloading metallic pistol and rifle ammo