I used the lvl 33 Callies until I started regularly entering paid tournies around lvl 70.
IMHO the lvl 33s are the best value ball on WGT for players not competing regularly in paid tournaments.
As to your request for input regarding varying meter speeds using the same ball, the meter speed varies no matter which ball is used, even during a single round.
Times when one has a clutch putt or approach and the meter decides to smoke crack is frustrating, but appears to be programmed as part of normal play.
I've been mostly using the lvl61 Nikes and now the same lvl TMs and went a long period using the lvl48 Nikes. Both these balls displayed the same propensity to either randomly slow down or speed up.
Just as some holes, mostly par 3s are more sensitive to an off ding shot than others, meter speed also varies. However, unlike the variance of sensitivity on some holes to off ding shots which doesn't vary, meter speed variation is random.
Don't ask me why because I don't know.
Mike