Hi Graham, a few thoughts:
* With the 9.25 you can possibly manage a bit more image scale, maybe up to ~0.12" per pixel or so? But regardless of that:
* Using Firecapture (I don't know SharpCap) you can set a cut out around the planet, save huge amounts of space, instantly align on the planet, and help maximise the framerate if file sizes are the limiting factor (rather than planet brightness). Keep the histogram reasonably high, but with exposure <~15ms (ideally ~9-13ms), but don't massively overdo the gain for a high framerate - a balance is necessary.
* you can certainly do
single video sequences of a minute or 90s or more without issue - longer if your image scale is smaller. Autostakkert's feature alignment easily corrects out rotation at your image scale. I image at about 0.08"/pixel and can get really hi-res on good nights with 60s videos, collecting up to 5-6000 frames per capture. More frames = lower noise of course, even if you only keep 25-30% of them.
* Gently balancing noise reduction and sharpening makes quite a big difference, whether in RS or postprocessing. E.g. if into photoshop, reduce noise before sharpening, as the sharpening process will enhance noise.