I have AP 1600GTO with PEM training running around +/- 0.74.  I have a 14” Edge HD @f11 and imaging with STXL 11K and guiding with its SXTL filter wheel/guider.  I use Maxim DL with 8/8 X/Y aggressiveness.  Guide calibration is 4 sec and 4 sec for guide exposure.  My guiding is +/- .5 arcsec when watching the guiding trace.  My imaging with narrowband is typically 20min in duration.  Early on I noticed my STXL fan was creating vibration and causing oblong stars.  I now run with fan off, but it does go on when it reaches a critical point.  You may want to try running with fan off too.

I’m enclosing a sample of what I’m getting with this setup.