Don't know abut the Giant Scale Planes kit or ARF or whatever it may be. If they recommend a .90 you can be sure that a 1.20 will probably be just fine. Most recommendations for engine size are intended for flying at a standard atmosphere. 65 deg.F, 29.95 barometer at sea level. If you go by the adiabatic lapse rate the temp will drop approx 3 degF per 1,000' and if youhave a higher temp your density altitude will increase acordingly, in which case the extra bit of HP will come in very handy. Just because it's there doesn't mean you have to open the throttle all the way.