size of the fuge is important. I used to have a 0.5 swing with a 20g sump under a 125g tank, then I got a 55g sump and had more room for macro and it cut the swing down to 0.2
How much swing is okay will also depend on your critters. Starfish and other echinoderms are more sensitive to swings than most fish, etc.
Right now I have my Reefkeeper set to drip kalk when pH goes below a certain point and now my swing is down to less than 0.1