So you averaged 6 passes per skate? That's a lot.
Your statement "Getting 40 pair of skates out of one sharpening ring is only reachable if you're exclusively sharpening your own skates by basically maintaining them every 2-3 hours of skating." is somewhat misleading. If you exclusively sharpen your own skates every 2-3 hours of skating, you'll get over 50 close to 60 'pairs' sharpened at an average of 2-3 passes per skate. That's what I do.
It's 320 passes per ring, use them however you like, that's how long a ring lasts. And the amount of material it removes per pass is fairly significant, at least when compared to the ProSharp for example.
You might be better off with a traditional machine like a Blademaster 850 if that's the typical type of usage you're going to see. Would be a lot cheaper in the long run.
colins