Hi Rick
Nice to see a fellow Paramount owner, I generally do two 15 star T-point mapping runs mainly due to time constraints and the changeable weather here, also I use a portable setup so I do this each night I image. I dream for a permanent setup in an observatory but that may have to wait. Originally I had a Meade LX200GPS so I was used to a maximum of 30 seconds unguided. Since changing to the Paramount and starting with 1 then 2, 4 and now 10 minute unguided subs I can see what you mean by not finding a limit. The only limiting factor that I can see is a cloud or the accuracy of the polar alignment. It will be 20 minute subs for me next time.
Best wishes
Gordon