okay, here's horrible... I have a handfull of very nice, what I would consider high end 1911's (Including a long slide Matchmaster with exensive work, , a colt and a Kimber), a DE in .50 AE, an S&W 46x, Beretta 92 and 92S, a Luger, an XD45 and XD9, and the standard hodgepodge of LCP, PPK-S, Bersa Thunder 380, S&W Bodyguard 380 type stuff... All of which shoot better than I do, but that's a given.
I also own a ransom rest, with many many grip plates. The single most accurate handgun ever fired in that rest, (Including a TC in .45LC, was, and still is, a STAR Firestar in Stainless, in .45 ACP. It was for all practical purposes, a single hole group at 25 yards, (.502") and right at 1" at fifty. (1.09") It's a crappy little gun that weighs a ton, is ugly, and doesn't feel good in anybodys hand that I've ever handed it to. But holy cow is it an accurate little monster from a rest. (I also don't think that the accuracy is based on it being a .45)
That being said, My Matchmaster is the best grouping gun that I own when I am plugged into the circuit. It is a Safari Arms model from back in the 80's before Oly took them over, and I carried it all over S America as my primary sidearm, so it's taken a pretty good beating a few times.
On the .45 accuracy arguement, I remember being told, (and I don't remember by who, but I think it's in my reloading book from Speer), that the .45 was the most inherently accurate bullet design based on external ballistics. The problem with that for me is that ballistics are different for a 185gr plug than they are for a 230gr HP, etc... Ballistics will also differ when fired from a rifled barrel vs. a hex barrel. and on material of the slug (or so I'm led to believe) . Based on these little unmentioned details, I would have to look very doubtfully on any statement claiming that a "caliber" was more accurate, vs. a statement claiming a certain "projectile" was more accurate. and then that all goes to hell when you mix in range and velocity! (the whole arguement just calls for more wood in the stove and another libation...)