Lovely images Paul. Kudos to you for the effort you're putting in. Saw those reflections in the other post - interesting. I'd probably be focusing on the secondary light shroud/housing. Perhaps create an aperture mask and tape it on to see if that alters the situation. Keep at it.
Wha!! Why are people comparing an RCOS RC with a GSO RC? Different league all together. Sure they share the same optical design, but that's where the similarities end. A more comparable RC to the GSO would be those produced by Deep Sky Instruments -
http://www.deepskyinstruments.com/products.htm. Personaly, I'm keeping an eye on their 14" expected to be released soon. Sure, these are more expensive than the GSO's, but you pay for what you get. The name "
Ritchey-Chrétien" does not insist optical perfection - RC's are not all created equal!
If you're going to make comparisons with an RCOS RC, you'd want to be comparing it against something like the A&M RC's -
http://www.astrotechengineering.com/Default.aspx?ID=156.