Fourstroke is the ONLY way to go with a Cub. If you go two-stroke, fly alone because you'll kill yourself if you ever see/hear a fourstroke Cub. I think a 54 is fine with the Cub but it would be TOO scale. It's not bad to have a little more power... seems to come in handy just when you need it. If you are looking for a budget fourstroker, the Magnum 61RFS or 70RFS are not bad. I had a 61RFS in an 8lb .40 size Cessna and it was fine. I think the GP cub is around the same weight with even larger wings. Of course, if you haven't budget limitations, I'd recommend a Saito 90 or 100 Twin. That would be absolutely tasty. If you do go with the Saito, you must post pictures!!!