Since your loads are pretty light 6hp and 2HP, you can go with light feed wire like 8AWG, but if you have larger loads later, you will need to upsize your feed wire. I assume you picked a 20HP unit because you are thinking that you will have larger loads later on.
In order to take advantage of the full 20HP, you would need a much larger feed circuit.
20HP * 2.8 a/hp = 56 three phase amps.
56 * 1.73 = 97 amps (square root of three to get from three phase to single phase)
If you ever had 20 HP of load motor at FLA, it would be sucking 97 amps single phase. You then have to add the idling current of the idler, probably about 10 amps for a 20 hp idler, so the total draw is 107 amps. I would use a 120 amp feeder and be done, but a 100 amp would probably be fine.
If you get a chance post some pics of the internals of your pannel with component ratings. The gold pannel I saw in the past was very nice, but I think it was a 10 HP unit. Just curious what is in a 20HP unit.
-Joe
