.45 ACP can also be shot in ESP. .45 ACP ONLY in CDP.
I'd go with the longer barrel, for competition. Longer sight radius, higher velocity for a given load.
Is anyone making a reasonably-priced 10-round magazine in .40? If you want to shoot Limited 10 in USPSA Competition, lack of 10-round mas would be a drag. If the new USPSA Single Stack Division gets some traction, a single stack .40 would be great for IDPA and USPSA, and you wouldn't have to buy different holsters, belts, pouches, etc.