@crswll@avandecreme@msalsbery We went with 256 back in 2008, but yeah, it's probably time to move up to 512.
The super tiny tiles below level 6 make sense for DZC files, when they all get jammed into a single image; that way you can load a multi-thousand item collection with just a few server calls. Of course we still don't support DZC in OpenSeadragon (yet!).
As far as I'm concerned, the key thing is to load a small enough level that you get the entire image in a single tile. Otherwise you get the "loading chunks of the grid" effect that breaks the illusion that it's all a single image.
Seems like a good optimization would be for OSD to figure out what the largest level that appears in a single tile is (it's different for different images, based on aspect ratio and tile size), and start loading the image from there.