There's no one scope to rule them all unfortunately
Depends on what you're interested in imaging, Ben. Your 8se would do a good job with planetary imaging as-is. The AT65EDQ is always going to give you a much wider field of view...that's a plus if you want to image big things, not so if you want to image small things.
IMO the setup of the mount, i.e. getting very good polar alignment, will be key to getting usable subs out of the C8. The AT65 will be more tolerant, but at f/6.5 you'd probably want to be exposing for longer than 2 minutes on anything but the brightest of objects, in which case, you still need good polar alignment. Guiding is no substitute for that, it just helps get around the periodic error manufactured in to affordable mounts.