I'd need to know what your friend means by "a scale airplane." I agree physics applies to everything and there is no magic dividing line between a scale and non scale plane.

Also I'd like to know exactly what you're looking for in a "high speed stall?" Do you expect a snap roll? Do you want the plane to just "mush" forward or in a gentle pullout?

Very much depends on these factors:

sharpness of leading edge
wing thickness
wing loading
"normal" stall speed
lateral balance

From my experience most modelers typically do not want to deal with a high speed stall, and therefore limit their elevator travels so at the highest speed possible the plane will not snap out of a loop (or turn). That's traditionally how instruction manuals would direct the modeler to set the max throw for a (non 3D capable) plane.

If you want 3D, of course all that goes out the window, and one must deal with the post stall (high alfa) flight regime of the wing.

Not sure how to make it sound simpler than that without addressing specifics of your original question which you haven't provided.