That a nice FWHM Colin
Since you are using a premium mount my guess is that most of the time you are seeing limited and much less often image scale limited.
What I was curious about is how far we can push image scale until we become mount limited.
I remember that my AZEQ6 could occasionally guide at 0.4 arcseconds RMS, but usually was guiding at 0.6-0.7 RMS, so there would be not much benefit in imaging at 1 app with it. Since RMS error is for 68% only, guiding would be +-1.2 to +-1.4 arcseconds at all times = about 2.5 to 3 pixels error in total at 1 app (given there are no unexpected sudden large guiding errors). So light that should fall on one pixel would end up on up to 9 pixels on good nights.
Greg - I totally agree with you. 1 app is the target but few have mounts that will accurately guide to take advantage of such image scale.
My conclusion is that we can often aim for large scopes that will give us excellent image scale for those rare nights with exceptional seeing, but rarely we carefully take into account our mount's typical RMS guiding errors.