Hi,
I also have an 8" Quattro.
Please be aware that the coma corrector here:
http://www.teleskop-express.de/shop/...pe-ab-f-4.html
Is also sold by Skywatcher and is available at Astro Pete's in Brisbane for $349 - way cheaper than getting it from Germany.
I have found it is perfectly corrected to the edge of an APSC chip - may go bigger but I don't know as I don't have a chip any bigger.
The caveat is that collimation MUST be bang on with ANY of the longish coma correctors. If you are even a little off the stars will be out in one corner.
I had to remove sag from my Quattro focuser (these steel tracks are nowhere near as good as a Moonlight), round the ends of the collimation screws, put a steel washer between the screws and the secondary holder and put stronger springs in the primary cell.
I did NOT have to do that when I used an MPCC - this is much more tolerant of any collimation error.
The results to my eyes are no better than the MPCC. If I'd known what I know now, I would have stuck with the MPCC......
I also wouldn't bother going to the 10 inch - all you get is a slightly greater image scale.................not significantly so anyway.....
FWIW
Gary