I never really considered "mastering" for live performance...interesting concept.
A superfast limiter is a good idea, I use a hardware compressor on the end to catch all but the most obscenely fast and strong peaks.
The weird problem for absolutely maximizing total loudness in a live environment is that, because of the way speaker power handling works, it's more important to control average power output than peak. As a matter of fact, a limiter can end up reducing the total output you can reach by forcing the entire signal down to a point at which its continuous average level won't melt the speakers. Crown implements a smart RMS limiter on their Macro-Tech and I-Tech amps. Something like that is a smart move. That way you can set the amps to limit their continuous level while still pushing transients out at the full level that the speakers can handle for brief durations.