Jason, for all practical purposes, as long as there's time for the roots to actually do some growing before the plant goes dormant, it's fine to repot. Especially if you have a large collection, it's not very feasible to catch each plant at that "perfect" repotting time. But if you can, the plant will fare a lot better than otherwise. I prefer repotting before the root nubins stick out much because they tend to be brittle and easily broken. But that's just me compensating for my own clumsiness. At the point you're talking about is still a great time if you can keep from breaking the new roots in the process.
Rick, the key to it is right in the middle of your post, where you said it's critical for the plant to go into winter with a healthy root system. That really is crucial if you want good growth and blooms the next spring.
Traci, it applies to all of them. On monopodials, the best time is when new "root nubs" are just starting to bulge from the stem, as Jason said, and a new leaf is begining to grow. (On those, there isn't much other way to tell...) On sympodials, it's when a new growth has just started. So if you repotted when there was new growth, but no new roots yet, that's the perfect time.