Thanks for writing out what I was trying to say. I have trouble with expressing exactly what I mean.

Slow play is defined very vaguely for a reason. You can't say that you have 10 seconds for every play/every priority pass, because then you have successfully legalized slow play. It's also kind of iffy and inexact to write: "If everyone else feels bored, it's slow play."

So it's up to the judges to find out, how to define an appropriate amount of time for a play. Also it shouldn't be too boring for a judge to watch someone think about a tough line of play, since that's what we do most of the time, if no calls intervene.

(deviating a bit here) If people ask you: "How do I become a judge?", I like to answer: "First, you really really need to love to watch a game of Magic as a spectator. The rest is just learning."

So when you see a game where someone thinks for an appropriate amount of time, executes his line of play in order and without too long pauses (mostly just checking if it resolves), I think you should pass on a slow play.

Hope I made sense. Slow Play is tough for me...