I shoot 230gr lead in my 45c with some 231 underneath it and it shoots nice groups 2-2.5" at 20 yds offhand. Easy clean up. No pressure signs.
I think the main reason was to keep the size of the grip frame down. The G21 is much thicker, but I don't know about the X45 or the HK variants but I would bet they are thicker as well. Ten rounds is plenty.
Yes, I'm a 1911 man too. I have a Range Officer, and a SA Ultracompact. Going to pick up a LEs Baer Stinger this friday.
I want an M&P for a bed gun. I need something with a rail on it for a Surefire X300. Maybe I'll get a railed 1911 eventually, but for now I think I will go with the M&P 45.