I've just got round to posting my results of testing the William Optics 0.8 Mk II reducer on the Skywatcher ED80 for the Canon 350D DSLR. There is a difference in noise between the images because the one with the reducer was taken on a moonlit night.
The following images show the centre and corners but are shrunk by a factor of 2.
Without reducer (half scale):
(http://www.markshelley.co.uk/Astronomy/technical/ed80_no_red_half.jpg)
With William Optics MkII reducer (half scale):
(http://www.markshelley.co.uk/Astronomy/technical/ed80_wo_mkii_half.jpg)
The full size versions of the same images are here:
http://www.markshelley.co.uk/Astronomy/technical/ed80_no_red.jpg
http://www.markshelley.co.uk/Astronomy/technical/ed80_wo_mkii.jpg
Looking in detail, the stars near the corners appear a bit spiky - other messages on forums have also noted that although the WO Mk2 and Mk3 both perform well on the ED80, they do produce slightly spiky stars. Looking closer, the spikiness is a kind of chromatic aberration the tangential spike is blue and the sagittal spike is red.
The reducer does a good job but certainly doesn't turn the ED80 into a Takahashi!
Mark