As for Pancho, well, let's face it, he probably wouldn't have reached 140 with anything, at least not with that old motion of his. As you may well know percentage was big back in Pancho's heyday, and his motion and mindset reflected that. (In fact I've seen it mentioned that Pancho's regular 1st serves were more like Pete's best second serves!)
I've seen one match of Pancho's(his 112 game match, a 2224 16 1614 63 119 win over Pasarell at '69 Wimbledon) & in terms of power his serve doesn't seem anywhere near the league of Newcombe, Ashe or even Laver.
But as you said his goals on serve weren't to hit aces etc, but to get a high % in(he made 33 straight 1st serves at one point & served at 84% in the last 2 sets....I can only recall Wilander, Borg or Nadal getting those kinds of numbers so late in a match)
I can see why he had such legendary stamina, since he paced himself so well on serve. And backed it up so well with great volleys & overheads(think he hit more overheads in this one match than any player today hits in months)
Only lost serve 3 times, one in the 1st, twice in the 2nd(& it seemed like he basically tanked the 2nd set since he was infuriated by the decision to not stop play after the 1st set. Light was pretty bad at that point)