The differences have to be somewhat extreme for you to actually notice since you are an observer & not in the plane. I have seen degraded performance from engines and the model, most noticable during manuevers & landings.the less dense air affects the lifting power as well as the engine output just when you need it most.since warm air carries more moisture than cold air, the high humidity only ads to the problem. its well known in the full scale world airplanes fly better in the winter.