Hi John,
Looking at the eight cycle worm period you have provide – I would almost consider this text book perfect – certainly from an auto guiding aspect. I would say that +/- 1” is your baseline. Keeping in mind that guiding corrections do always correlate direct to the worm error as previously mentioned. There is obviously other factors such as the accuracy of polar alignment, seeing conditions blah blah (you not the stuff).
I heard that PEC on the Sphinx was a bit of a dud. Let hope they get it right next time. Ultimately, integrated PEC should allow you to record two or three runs and average them. I believe Gemini provides such functionality as do other telescope control systems. I only ever have one PEC run programmed, but it’s usually a very good one.
I would keep your guiding exposure times high so you don’t chase the seeing – between three and five seconds is good. Longer is better if you’ve got a stable mount that tracks well, but this also depends on your focal length you’re using.
Not sure how keen you are, but you can you can try swapping you dec worm with the ra to see if you get any improvement. The improvement would be very marginal, nothing drastic I suspect. As you mention, you could also look into further adjustments or regreasing to squeeze out more performance -
http://enzerink.net/peter/astronomy/....htm#radecworm