Not Urban legend... fact. Especially for up-elevator on an upward angled V.

I had a Coroplast mdel built by plans from the SPAD website. This particular model has a V tail.
The method for getting the V angle is by heaing and deforming some PVC to make the angle brace. As the PVC cooled... it sprung back toward 90 deg. I ended up with appx 95 deg angle V.

Up elevator at full throttle slowed me down like I'd killed the engine. Down elevator was not as bad, but it was noticeable.

I cut the bad V tail off... and put on a conventional tail. The same elevator deflection angle resulted in almost no noticable loss of speed. (of course a high climb angle always slows you down... but it was a HUGE performance change.)

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BTW... ideal V angle is NOT dependent on control function... it is an aerodynamic constant. You are making the V surfaces perform the function of a vertical and a horizontal. you need to geve the effect of the vertical area of a standard Fin/rudder and the horizontal effect of a standard flat stabilizer. To do this... the projected shadow of the V in top view would need to be slghtly larger than the flat horizontal originally was (the angle creates a little loss of effect) and the side proection needs to be just a bit more than half the original Fin/rudder. You get these proportions at...110 deg.