Did you miss this part?
not to exceed actual gross weight Vr+20 knots.
So, if RTOW Vr is more than 20kts greater than ATOW Vr, you may use up to Vr+20- as John has been explaining.
not if you're taking off at performance limited TOW. Whatcha gonna do then?
If you're performance limited, you're performance limited. whether you're in an Airbus or a Boeing.
But if you HAVE extra performance at hand, why not use it?