Not every ammunition maker is a member of SAAMI, keep that in mind. I would feel quite confident with ANY SAAMI spec load in a Glock 20. Beyond that, I really don�t see that you gain much with +P; maybe 100fps, but a good decrease in safety margin. Are you willing to give up a good deal of safety margin for 100fps? Do you think anything you shoot with 100fps less velocity will be significantly different from something that has the extra 100fps?
When you go beyond SAAMI, you�re trading safety for performance. It�s up to YOU to weigh the risk vs. benefit.
Personally, I can�t imagine there�s anything that is hit squarely with a full power 10mm load and won�t go down, but will with 100fps more. Color me dubious.
I say, if you�re carrying a Glock 10mm you�re the last guy in the world who needs +P�you have like 14 more chances at success available to you instantly.
