After 40+ years of shooting only Colt 1911s in .45 Auto, last month I purchased a Colt Combat Unit in 9mm mostly after listening to Ken Hackathorn's reasoning on the capability of a 1911 shooting modern 9mm loads.
After limited shooting, I must say I agree. The 1911 in 9mm is a great pistol. Mine has been 100% reliable so far, even with bulk Federal 115 gr. and the shooting characteristics of a 1911 chambered in 9mm are very nice.
The improvements in 9mm bullet design and loading makes the old .45 vs. 9mm debate pretty much a moot point these days.