I'd say Camacho was a class above, though Stevie was a very good Lightweight in the late 90's, the best outside of Mosley and maybe Castillo later on IMO. Camacho was just too fast for him in a nutshell, Stevie wouldn't be able to utilize his jab against Camacho's superior one, and Camacho's handspeed and combinations were far superior. He also had great movement and footwork, so I don't see Johnston pressing effectively. I like Stevie, but he's pretty much out of his league here.
steve was a very good fighter, at his best he was on par with castillo and i he was neck and neck with mosley in the amatures. i think this fight would be very competetive, from what i have seen of johnston, he was very effective of the punching through the gloves which could mean that his punches would connect faster then comachos looping flurries despite comachos supperior handspeed. steve was able to beat a very very fast southpaw in sharba mitchell. sharba is one of the most softspoken fighters in regards to handspeed. the prime sharba mitchells hands where very very fast and imo rivaled zab judahs and shane mosleys. he may not have had the power, reliable leg movement, durability and strength as mosley or judah but his hands speed was up there.
Camacho has too many physical advantages, but Stevie would own his ass on the inside the few moments the fight is conducted there. Camacho will simply hug and move and use his greater hand and footspeed to pile up points. Stevie will have his moments, but i don't think he'll take more than about 4 rounds. If they fought in a real tiny ring and Camacho had to stand and deliver, Stevie would be there all the way with him. A very underrated fighter, who I felt beat Castillo twice.