Bob, my Platt Spitfire flew with a ST2500 at 23 pounds and did OK. I would say it had pretty scale performance but it certainly was not a rocket ship. If your bird is only 20 pounds the 2500 (assuming it is a 2500 and not a 2000) should do a good job of flying it. Don't remember what prop I ran then but nowadays I'd probably look into one of the paddle blade APC props for it.