I carry a 21sf so I don't know.If they made a 33 round mag for the 21 I'd shove a few in in my car. My question had to do with using comfort as an issue being tossed aside. Everyone decides at which point comfort begins to trump firepower.
I know some say they choose firepower over comfort because when the chips are down "thank (insert deity) I brought my (insert kool-aid) and not my (insert bland water)" when in reality at some point in the game comfort ultimately wins out. The only excuse for not carrying a 33 round mag if you carry a G17 or G19 is comfort. You could shove one or two inside the pants or a man-purse if you REALLY wanted maximum firepower.