The point wasn't how far you should "push it", although if the unit got really too hot the protective circuits would shut it down. Limiting the power capability by limiting the voltage output leads to a possible situation where clipping would occur earlier and might cause speaker damage, a more significant problem than simply running hot.
Sound&Vision often tests the effect of the lower impedance setting during its reviews. The 806 hasn't been tested, but note for example the result with the
875 .
