Thanks Sheldon, good to know. My worry wasn't that a derailler designed for a 6-speed drivetrain was speed-specific, but rather that it was cable-pull specific - like pre-8-speed Dura Ace, or using Campy deraillers with Shimano shifters, etc.
I'd looked over your article before, and it says nothing about 6-speed shifters, only 7, 8, 9, and 10. Could you note 6-speed compatibility along with 7-10 deraillers in the article? It might help a few other strange souls who might use the old stuff