You forgot SIG. And it doesn't hurt me to say it. Lest we forget, SIG was quite heavy in the running for the U.S. Service Pistol and did quite well during extensive testing.
Here is the harbinger.
If you feel you must use +P+ ammunition to achieve the desired results in a chosen caliber, you have likely chosen the wrong caliber.
Not an eternal truth by any measure, but it should give some pause for thought.
I refrain from using Cor-Bon for defensive ammunition as my experience has it varying in consistency (velocity and accuracy), but have absolutely no problems firing most major manufacturers +P ammunition in my SIG's. I am glad you are (hopefully) experiencing better results.
I would like to test some +P+ from the major manufacturers just for grins, but have no desire to carry it regularly. Personally, I think the added expense of +P+ ammunition versus +P ammunition is hard to justify for a percentage point or two increase in performance (and whose data you choose to believe).
From standard velocity to +P I typically see a 25%-30% increase in price. From +P to +P+ the price typically doubles (due to scarcity/demand?). I prefer to have my carry arms around for awhile longer in any case.
Never fired any +P+ rated ammunition in my Centurion when I had it, so not much help in that department. I will say that I would not have hesitated though. I only sold the Beretta to finance another SIG...