Twin you said 'I now want to play a massive stadium gig to get the thing REALLY cooking!'
Sorry dude, ain't even gonna happen if you play a big stadium gig, especially if it's outdoors sound guys want the control now, so using a 100w head live in just about every situation you'll ever encounter it's not going to be cooking.
Attenuators are your friend, wattage just gives a different tone to be honest these days..
I play 35w Trainwreck clone live and I used an attenuator to get the volume down to reasonable levels and It's great. I've only played one gig where I didn't have to use the attenuator and that was just because I forgot it, over powered the band a tad in a 500 capacity venue.
Most amplifiers I build these days for gigging are 15w - 35w.. more than enough power.