I played around a few months ago with XFoil
trying to see what they predicted about reflexing the flaps on an RV. XFoil provides predicted 2D airfoil lift and drag, and AVL predicts 3D lift, drag, etc on a wing and tail.
XFoil, which calculates 2D airfoil performance, does show a small reduction in drag by reflexing the airfoil. For example, at a CL of 0.15 (typical RV CL at high speed), the airfoil section CD is about 0.0062 with flaps at 0 degrees, and about 0.0052 with flaps reflexed up 5 degrees. The lift for a given angle of attack is decreased too, as you might expect. This means the inboard wing will make less lift, so the outboard wing has to make more lift. You would think this would mean that the outboard wing would see a drag increase. But, the NACA 23013.5 airfoil actually has its minimum drag at a CL of about 0.45. So increasing the CL on the outboard wing might decrease the drag a bit. Of course there is always a pay back, and in this case the additional lift on the outboard wing will lead to stronger wing tip vortices, and that means more drag.
AVL does rudimentary 3D analysis (i.e. it attempts to account for the variation in CL along the span, wing tip vortices, etc). It predicts that the whole aircraft CD is:
RV-8, 193 kt, MSL, aft CG, flap 0 deg -> CD = 0.03424
RV-8, 193 kt, MSL, aft CG, flap -5 deg ->CD = 0.03651
RV-8, 193 kt, MSL, aft CG, flap + aileron -5 deg ->CD = 0.03875
Note: AVL was originally created to do analysis of RC gliders, so it assumes that the fuselage is of circular cross section. This means that the fuselage drag, and fuselage/wing interference drag is not correct, so the absolute values of the whole aircraft CD are probably not correct. The variations between conditions is probably reasonable though.
Summary - there is probably little benefit from reflexing flaps and/or ailerons on short wing RVs.