You can do interesting things with a 68040 machine with a nubus Charger dsp card, or a Radius Thunder IV GX card (with the dsp plug-on card), or an 040 accelerator with the similar dsp card (there were various models, but they are now v.v. hard to find), or indeed, an AV 040 Mac (which has a dsp on the logic board), but even then photo editing can be slow, as dsp acceleration is limited to certain filters. It can, however, be done, and it is pretty fast if you limit yourself to the supported software.

Scanning itself is certainly acceptably snappy on my Q650 with Quad 040 accelerator and Charger dsp card. It's no Mac Pro, but where's the fun in using one of those?

I did this (and following) on it, with a ColorOne 1200/30 - and no, I don't run the site.