[graham.hobart (Graham stevens)]

ten and twenty min subs with no star trailing would indicate very good PA with good guiding to limit field rotation.
What I would bear in mind how ever is you may have to increase your Starshoot exposure time if the seeing isn't too good, to allow the better acquisition of guide star.
That's just what I do (or did when I used PHD) when it's a bit murky/ poor seeing.