I honestly think he loses to both. Johnston & Nazarov weren't necessarily better than Loma in a P4P sense, but they were better lightweights. Stevie was a lot physically stronger than Loma, and with Loma lacking the power to deter him, I just see Johnston getting inside and outfighting Loma. With Naz, I see his bigger firepower and straight, accurate punching busting Loma up.
I haven't seen much of Johnston, so I'm interested in what others think of him and I'll leave my opinions on him out. But I do think Loma gets knocked out by Nazarov, who's a bit of an unheralded beast.
Most of Stevie's best performances are on YT, I believe. Here are two of his better ones. The Manfredy fight, and his rematch with Cesar Bazan:
There's actually one more prime Johnston performance that I found on Daily Motion. I'll pull it, and upload it to my YT page later today, so look out for it.