First sit down and dust off your wallet. Then go looking for Columbo or Pensky spindles that will run from a 400 HZ VFD. Then find a commercial VFD that will do up to 400HZ. There are a lot of big spindles but most use a much higher frequency drive and you have to match the drive to the spindle. A HF spindle can be cheap but the drive will make up for it.
5HP Columbo's are several thousand. They will cut 3/4" material in one pass all day long.