I have a lab quality Corning stir plate that I use for my starters with my 5l Erlenmeyer. I could never get the speed up over 8 (out of 10). It would religiously kick the stirbar off at a hair over that setting.
Today was my first try with a few small drops of defoamer in my starter. Now I can crank the speed all the way, and it runs like a charm. It is also noticeably quieter. It may be a co-incidence, but after 10 repeatable results, the only thing different here is the defoamer. Maybe something for people to try.
This place really went to hell. Follow the OF standard stout. Bye.