I am a little confused. Leaving Big Bertha out meant that the mirror didn't need any time to cool. After the adrenalin rush of manufacturing in Delrin, I couldn't sleep, so I went back to trying to debug Big Bertha's optics.
Using an aperture mask at the front of the tube definitely helps. Without it, Saturn was definitely blurry at 160x; with it, Saturn was still showing an okay (not great) image at 222x. Cassini's Division was visible around the planet, but not dark; the brown cloud band was visible. Jupiter was still low in the sky, but with the front tube aperture mask, I could see quite a bit of detail (fleetingly) in the clouds.
Tonight I will put the mirror masks in place, and see what happens. Part of why I am now a little skeptical that the problem is turned edge is that star testing no longer shows the single bright outer ring outside of focus. This seems to have gone away after I added three more supports to the mirror on the edge--but the image still leaves much to be desired in crispness.