I was out just last night with my KP and the 55-300mm PLM. Although I could have, I didn't employ the Astrotracer, figuring I could get some decent exposures without. After about a dozen shots, the longest I had the shutter open without easily seen star movement was 4 seconds. Anything longer and movement could be seen when enlarging the image.
In theory, the "500" rule ( 500/(Crop factor X Focal length) = Shutter Speed ) would limit exposure at 200mm to 1.7 seconds with a 1.5 crop factor... I saw that could be fudged somewhat.
Here's the comet at 260mm on my KP at 4 seconds, f/5.6, ISO 3200:
Cheers, Allan