I wouldn't be surprised if Armstrong beats all of these guys. The one exception might be Duran at welterweight, as Duran would've had something of a size advantage there (Armstrong was never really more than a jr. welterweight). Armstrong was at his peak around super-feather, and anyone around there I would favor him to beat. He was just that damn good.
Saddler has shown trouble sometimes with fighters who got inside his long arms and gave it to him on the inside (see his fight with Charley Riley). And Armstrong certainly has a great chin - Ceferino Garcia couldn't back him off, and he was one of the hardest hitting welterweights-jr.midddleweights ever. I would think Armstrong had what it took to keep on top of him and outhustle him to a decision.
I know, Ive seen really old stuff, grainy footage of both but undoubtedly the clearest stuff was when they were a bit (tho not miles) past their best. I think Pep vs Armstrong would be the ultimate clash of styles, the boxer vs pressure fighter always brings out the best of both & these 2 sit at the very top of tier no1 when it comes to being the best at their own style. Its possible Armstrong might be too big naturally for Pep but if he isnt then this is too hard to call with any real certainty.