I just got my Saito 120S for this airplane. I'm having second thoughts due to its great weight and size. It appears that I will have to move the fire wall back 1/2 inch and may have to add up to 2 oz tail weight with the servos and battery in the far back of the radio compartment.

Should I exchange the engine for the 100. This will require no fire wall modification and may be up to 14oz lighter after balance consideration. I'm not sure if I need the extra power either, as I don't fly 3D. I do need adequate power for IMAC basic though.

Wing loading w/100~19oz/sf, weight ~8lb
Wing loading w/120~21oz/sf, weight ~9lb

Did I get the wrong engine?