Dunk, I could not get rid of flexure-induced 'creep' on my C8 when using a guidescope. Evidence:
http://www.iceinspace.com.au/forum/s...d.php?t=124484
So I switched to an OAG. It works a dream, now I can readily do 20+min subs with round stars. And it would suit your QHY5L-II (which is very sensitive, and has the same chip as my ASI120MM).