Its somewhat reassuring in some ways to hear those with permanently mounted high end gear still have to deal with these issues.
For those of us with cheaper mounts on temp to semi-permanent piers, there is always the solace that a little bit of DEC drift is probably good to avoid backlash. Pole Align Max and drift aligning seemed the most reliable and closest in agreement for me over the years. PHD2 polar alignment module is a great piece of work for those operating outside the SB or Maxim paradigms.
Would be very interested if anyone has references to calculators for drift, and possibly maximum guiding excursion. Presumably if you fed in focal length, FOV, guiding exposure and sub exposure it would be possible to calculate:
1. Upper limit for sub exposure for a given PA error (above which field rotation expected)
2. Upper limit for guiding exposure for maximum expected PEC/guiding excursion (again, likely to only be an issue for cheaper mounts with greater worm/PE concerns).