Well, Steve proved himself to be a very good, skilled and worthy Lightweight over time. On the other hand, Pacquiao beat David Diaz at Lightweight, so I'll have to with Pacquiao.
Johnston was pretty tough and he was crafty, I think he'd go the distance... He's too close-range to beat Pac though, Stevie was a hustling, close-range boxer... He'd get some rounds, but I think he's too happy to get drawn into a trench battle, where Pacquaio's speed and power are really a major factor... I think the pac-man takes it pretty fucking cleanly