Unless you're shooting Open / Unlimted then 19 -20 rounds will be fine. I used to shoot Limted in USPSA and Tac Ops in 3gun. Used the same pistol for both. I really wasn't at a disadvantage even though I was down 3 rounds from the 9mm guys.
I shoot my 2011 in .40 and only load 17-18. All of the 3gun matches that I shoot aren't pistol heavy on the stages, and even if they are I can plan a reload while moving so it doesn't hurt me. However, the more the merrier I guess they say.