I run a #22 spring in my g20 with hot loads down to sub sonics and have no problems. The 20 came before the 21 and had a heavier slide, when glock built the 21 on the 20 frame they had to lighten the slide to get the weaker 45acp to function. I would stick with the heavier spring to keep the barrel locked up longer and look at your extractor instead.
Just my 2¢…
"A free people ought not only to be armed and disciplined but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government." --George Washington