It will vary by material and diameter:
Bigger hole = slower speed.
As a general rule, man-made boards and softwood = faster RPM (not necessarily faster feed speed).
Don't let the bit rub - the wood burns and the cutting edges blunt. These things don't cut sideways - if you're not making a hole perpendicular to the surface, arrange a wedge so that the bit enters wood as perpendicular as possible, AND clamp securely, so the stock can't slide around. When the bit rubs at the side of the hole and overheats it dulls-off the rim of the cutter, which is where the cutting action is most crucial.
I know someone will immediately say at this point, "but I do that just fine.", BUT I don't think these things are suitable for handheld use, except in the small sizes. I have trouble with them in a proper pillar drill. Holesaws for handheld, Forstner in pillar drills, and with care.
Whenever I use one handheld I usually regret it: I'll chew up the surface, or splinter it, or the bored hole won't be straight, etc. or it will burn the wood.
For anything smaller than 3/4" you'll get much better results with a hand-powered brace and bit (as long as the spur is properly sharp). Larger than 1": holesaw! There's nothing to stop you starting with a holesaw (to get a clean entry), then continuing with something else.
Two tips:
1. experiment on scrap to get the right speed.
2. cut a guide to clamp onto the stock over the hole. It reduces breakout, like a tight-mouthed plane does. For a very neat finish, you can scribe the circle with a sharp-point of a pair of dividers first (or a cut-off knife blade in a pair-of compasses arrangement, on a tangent), but that's a rather tricky operation - one slip and you've made matters worse than not scribing.
