Just remember, when applying weight penalties for take off due some unserviceability, like anti-skid U/S, for instance, that the penalty comes off the WATlimit for that runway, (Weight, Altitude & Temperature), which can be well in excess of the MTOW and does not come off the MTOW unless otherwise stated in the AFM.
Saw a flight cancelled once because the penalty was applied to the MTOW and not the WAT limit, when the WAT limit was well in excess of the MTOW and a max weight take off was possible, subject to landing performance of course, which in this case was an even longer runway!