I am fortunate to have a Bosch 1617evs variable speed plunger router. For some reason I never utilized its variable speed capability. In my younger days as a machinist, I recall numerous charts and reference material which would allow machines to be adjusted for RPM and optimum feed rates taking into account various materials being machined.
Based upon my previous metal working experience I decided to use the speed adjusting capability and see how it worked. My routers speed adjustment is graduated in numbers from 1 to 6, 1 being equal to 8000 RPM and 6 equal to 25,000 RPM. My experience has been very favorable. As a general rule the smaller the bit diameter the higher the RPM. I use 1/2 inch straight slot bits frequently and running them at 16,500/20,000 RPM works very well. The bits seem to last longer, produce a better finish and the noise factor is significantly reduced. Some recently purchased, inexpensive, two flute HSS end mills seem to work a lot better, and hopefully will last longer between sharpening.