The comparisons are already being made this weekend, so let's have them go at it here. P4P is almost pointless since they'll now have fought at the same weights after this weekend. Armstrong's lone foray into middleweight came with his weighing in below the WELTERWEIGHT limit, so... pick a weight, any weight.
You talk about an impossible comparison to make. I know it's ridiculous for me to state that they fought in completely different eras, but these guys REALLY fought in different eras. Imagine Manny, as great as he is, fighting 3 times in the same month with the final fight being against a guy the caliber of S.R. Robinson. Or imagine Manny trading punches with Barrera for 10 rounds and then fighting Marquez 2 weeks later. That's the kind of shit Armstrong did on a regular basis over an almost 150 fight career. I have no clue how an Armstrong-Pacquiao fight would unfold, but I won't pick anyone over Armstrong between 135 and 147
I think both fighters peaked at 130-ish. Pac hit his peak in the 3rd Morales fight IMO, and Armstrong was typically fighting a few pounds north of 126 when he seems to have hit his stride in 1937. Either way though, I think your prediction is a fair one.
I'd take Armstrong by stoppage at featherweight, in one of the most brutal fights ever. Both were massive punchers there - Pacquiao being the harder of the two - whereas only one had a great chin. Marquez hurt Manny in their first fight, and Armstrong was clearly a bigger puncher than Juan, and a much more persistent finisher too. At 130 to 147, Manny's defence, footwork, chin and techniques all improved. Enough to where he probably doesn't eat as many clean punches (but still eats a lot), and lands more of his own, making it less one-sided - and less entertaining due to less clean punches landed, although it'd still be undeniably violent - but he still loses a clear decision IMO. Armstrong's dirty, gritty pressure fighting is just gonna be awful for Manny, since he can take Pacquiao's punch. Think the Horn and Hussein style match ups, buy if he was in there with Henry fuckin Armstrong, not Jeff "PE teacher" Horn.
JM struggled with Diaz and Katsidis at lightweight. "Homicide Hank" would live up to his nickname against Marquez.
Yeah, it's those fights why I think it'd be great. Like Marquez constantly in the state he was when he got up in the third round vs Katsidis. It'd be a great fight IMO, but Marquez stands no chance of winning.