Hello Hauke!

  HF> ...I don't know about 4 bit greyscale, though. You probably have
    > to have 2 MBytes VRAM in the box or live with 1 bit b/w.

I would normally expect 640 x 870 x 4 bits to use less than 272 Kb,
and I think the stock Quadra 700 comes with 512Kb VRAM.  That said...

         http://docs.info.apple.com/article.html?artnum=10992

...makes interesting reading, and gives at least one example where a
mode uses more video RAM than might be expected.  I'm not sure how
relevant that example is to greyscale modes though. Perhaps nobody has
needed it enough yet to write support for it.

  HF> I started off with X11 on an SE/30...

Someone brought me some SE/30s the other day.  The temptation to try
NetBSD on one is nibbling away at me (probably without X though ;-)

Regards,
  - Andy.