Every fraction of a second counts. The shorter the stage is, the more important that reload is (like classifiers).
In terms of mag sizes, I have a full range of 140,155 and 170, and use whatever is most appropriate for the course of fire. 140s change faster than 155s, which change faster than 170s. I would say most of the time I start with a 170 and reload to a 155, but there are times I may even start with a 140, take 4 or six shots and then change to a 170. It depends on when the mag change is most efficient for the particular stage.
I routinely change springs on these mags every 2-3 months and whenever they hiccup or bind. If that doesn’t resolve it I also change the follower.If that doesn’t resolve it, tube needs to be inspected/measured. I routinely change the follower on these mags once a year. Disclaimer: I shoot open 9 Major which is very sensitive to mag/ammo issues.