Frodo wrote:...Clearly, zooming in takes more horsepower, and I don't know either just why it seems to take *so* much more. I'm a little surprised to hear about this in 6 only because of the Cocoa graphics update.
Well you guys are better at the deep down internals of software than I ever was (aren't you?

) but I would expect performance to suffer in a highly zoomed in state. Redraws in any app are going to suffer similarly.
It may also be dependent on other factors, such as what you're zooming in on (MIDI vs. audio) and how many tracks of each you have. If you have, say, 6 tracks and you zoom into one, perhaps DP is expecting you to switch to another track at the same zoom level and is preparing that view in the background?
That is, of course, only a lame assumption on my part, but in my fantasy world, I always assume something like that is happening at the software level. Another example is Photoshop. It seems to take a very long time to redraw a zoomed in, hi res picture. This is particularly true using a plug in like "liquify" where so much happens at the cache level before saving to disk.
All that hyperbole said, like Frodo, I don't playback at an extreme zoom level except if I'm really bored and want to watch the cool graphics speed by (which are essentially unreadable by this simple human.)