Just don't think that you can crank your amp because of the cab rating.
As stated, the "thermal rating" does not even come close to what your cab can handle in the real world before suffering physical damge.
Additionally, if you crank your amp, you can be sending power way above what your amp is rated for, so the best answer (as always) is to listen with your ears for signs of distress.
Life is good as a "Bottom End" dweller
Mesa Boogie Club #92 / Big Cabs Club #37