It'll fly fine at 13 lbs. mine flies VERY scale even with the 1.60 up front. I do most of my flying at 1/2 throttle or less throughout most of the flight and only use full throttle on uplines.

Other than the engine thrust issues I touched on earlier I would recommend that you seal the control surface gaps, especially the ailerons. The ailerons are sort of small for such a large wing and need all of the help they can get, made a huge difference on mine.