I've been imaging with a Meade SN6 but have thinking about moving up to a 8" f/4 Newtonian. I wasn't sure how my Atlas would handle the load, so I borrowed a similar scope from a club member. I did a 45 minute guide test with each scope back to back and did some analysis using the PhD log and a statistics package. I computed distance from the target centroid using the good old Pythagorean theorem at each log entry (sqrt of dx^2 + dy^2) and did an analysis of guide performance using that metric. Results are attached.
I'm guiding with the SSAG and 50mm finder.
You can see that the guide performance was basically identical for the 13 lb SN6 versus the ~18-20 pound 8" Newt. I also had to add another counterweight for the Newtonian, so the mount had quite a lot more weight on it in that configuration.
Seeing was poor tonight (2/5 by CSC), so absolute guide performance wasn't great.