You've got it all wrong. He used 200 watt speakers to get zero speaker distortion.
Not 100% sure if he was using EVs in the El Mocombo days... but you're right in the sense that he was all about clean head room. His Fenders were modified w/higher wattage power transformers to give him that loud & clean tone w/plenty of head room. He wanted to be in control of the distortion. So, that's where the TS-9's came into play (2 of them). Later in his career he moved to the Dumble SSS & Marshall Major (both high wattage amps w/plenty of headroom & 4x12s loaded w/EVs. He also used very heavy strings to get that "thump" and that was very hard on the speakers/amp.