I think "Revelations" by Cryptoburners is a particularly bad-ass slideshow, amazing it runs on an A500. If you have a gfx board, "The Castle" by loonies should run on your A3K, and would definitely make use of that '040. (It's kind of tough to find OCS demos that requires extra horsepower beyond 68000, and not a whole lot of 68k+gfx stuff. Regardess, there is _ton_ of good OCS material IMHO.)
Also... in case you haven't checked it out, the
Amiga Demoscene Archive is a fantastic resource for finding good demos... nice thing is you can filter by chipset. Seems there are a couple of relatively new ECS demos that look promising.
