A few years back,a past member of our local R/C club had a GP Ultimate 40 as his second plane and threw a Saito .80 in it.Flew fine as long as you kept the power up but drop the power a bit or better still......dead stick,it would drop like a friggin brick.Extra power at the expense of increased wing loadings=crappy flight characteristics.The secret to success is to achieve the best all around power to weight ratio possible.Slapping on a bigger heavier more powerful engine is sometimes the very thing NOT to do.When all is said and done......to each his own.