Thanks for digging up the information. That puts Magic Tape even closer to 810. They certainly look like they are twins, side-by-side. 3 mils is about as thick as air. Really, though, the exact mils is not that important a variable. I use the same puddle pushers for all my coating. 10 wraps of 850 tape. Might be eleven or twelve on one of them. (I have five so that I can coat five 36" strips of film in one coating session, without stopping to clean them before I'm done. With film, starting with a dry puddle pusher improves the quality of the coating pass. With paper, it's not as important.)

Anyway, what's important is the temperature of the emulsion while you coat. One degree C can make a difference there. It's all about viscosity. The lower you can go and still have a good, smooth flowing emulsion, the better the density and contrast in the final product (permanent caveat: "in my experience".)