Okay then, I'll give an example of the sort of calculation I'm thinking. An extreme example and most likely unachieveable for me, but its always good to challenge yourself, and as they say "imitation is the sincerest form of flattery".
Anyway...We have Mike S's sensational Virgo Galaxy photo
here. He has a total integration time of 240mins, using his AG12 at f3.8 with a KAF16803 which has an image scale of 1.63 arcsecs per pixel. The size of the Airy disk with his scope is 1.09 arcsecs (according to this calculator
here). I'll use an averaged QE of 55%
My scope is a VC200L with focal reducer (200mm aperture, f6.4), and a lowly (comparatively laughable) Canon 400D. The image scale is 0.92 arcsecs per pixel. The Airy disc with this scope is 1.64 arcsecs. I will optimistically assume a QE similar to the 40D listed
here of 33%
So 240mins x (f6.4/f3.8)^2 = 680mins. To account for the difference in QE, 680mins *0.55/0.33 = 1134mins. The full well and read noise of the KAF16803 is 100,000 and 9e- respectively, while for the 400D at ISO800 it is a measly 5611 and 5.2e- respectively. The dynamic range of both is 11111 for the KAF16803 and 1079 for the Canon. Not quite sure how to factor this one in - perhaps it means that I should scale my subs by a factor of 1079/11111 if I want to preserve the dynamic range that Mike has, although that would probably mean that Im only taking subs of about 1min (assuming he was using say 10min subs) which means i'm probably missing out on the faint stuff. As far as theoretical resolution goes, possibly we are similar - he is limited by his image scale of 1.6", where as I am limited by the airy disk of 1.6" also...?
If I were to upgrade to say a KAF6303, that would change my image scale to 1.45" (so still limited by the Airy disk) however my QE would go up to something like 65% and with a full well of 100,000 and read noise of 11e- my dynamic range is now at 9090. Because of the increase in QE my exposure has dropped from 1134 to 576mins. Also, I can now possibly take ~9min subs to Mike's 10mins and maintain a similar dynamic range. Resolution as I understand it would still similar at about 1.6" in both cases.
I could have made some mistakes in the above and I apologise if that is the case, but it hopefully gives a practical example of why I've been asking these questions.
(btw - I realise the FOV will be different for the two scopes above. I'm also aware that the KAF16803 is mono and my existing camera is OSC and that in itself will result in a resolution cost. Obviously the above ignores seeing effects as well)