If it cuts through consistently, then that sounds pretty good. I'd have guessed 15-17 speed, 100 power, 500f for a 35W Epilog when cutting 4mm plywood. Typically, you can cut faster but won't necessarily cut all the way through everywhere, and even a few areas that require hand work to finish take enough extra time/effort that its generally worth slowing down the cut to ensure consistent, complete cut-through. (Unlike with DC glass tubes, there's usually no need to run less than 100% when power-limited cutting with an RF metal tube.)