I'm a speed sewer. I get impatient with slower speeds. My speed setting is set to "rabbit" permanently (It's a Juki so the settings are between a rabbit and a turtle, LOL!) You can totally sew accurately at high speeds. Hold the fabrics above and below and just GO from point to point. You will get a straighter, nicer line than if you were plodding along. Love the high speed for sashings and borders, but really I use it for anything.
On my longarm, I sew at 85% to 90% of the max. Gotta get those puppies done!