I agree with Paul, I really don't think there is a hard and fast rule you must stick too.
On the night of Anthony Wesley's discovery of the Jupiter impact nearly 7 years ago.
I and a number of people were observing Jupiter in my 16" through mist at 700xmag and the detail was extra ordinary.
The Oooos and Arrrs coming from the other observers was testament to the magnificence of the apparition through the eye piece.
I am sure we could have upped the magnification but at the time I didn't have any eyepieces to do that,I do now.
BTW if we had observed Jupiter for about another half an hour we would have seen the "Bird Strike" visually.
Cheers
