The original Top Flite Flite Streak was intended to be a C/L Combat "trainer". .35-.40 size combat engines were used on these birds. For performance more like a stunter, then you use a .25 or so. The current Top Flite Flite Streak ARF model is listed for .25-.40 size engines. Your engine selection should be determined by what you want the model to do.

An O.S. Max .40 LA is not "too much" engine for the airframe. Just realize that the model will be quite fast.