Let me start by saying I'm no expert by any stretch of the imagination when it comes to cnc but I have been reading this board for a while and researching the plasma builds. From what I have read, a good ratio to aim for would be between 3:1 and 5:1 depending on how much definition you need. A good person to ask for a definative answer would be Tom at Candcnc.com. They make the electronics packages to cnc builds and conversions. Tom is a pretty helpful and knowledgable individual.