thank you for the comments:
@calico: the white dots are actually small reflections
@MacGuyver: thank you, and yes, I'd like to have the image rendered bigger as well, however I've hit a memory limit on my machine, plus the render takes awfully long for my taste ;-)
However I shall try a bigger render, hoping it won't crash. I would also like to test if it makes a notable difference to render at quality 1. I have assumed that the AA filter would eat the detail away anyway.
Cheers,
Frank