3.9-4 GHz is pretty much the limit for 1st gen Ryzen from what I've seen, even with the best mobos on the market, not sure if you'll be able to get that far. Either should be fine for some OC though. Doubt there'd be a significant difference between the two, I'd go with the steel legend personally.
Edit: Oops, though you were talking about he B450 Plus. I still don't think there'd be a big difference, but I'd lean towards the Asus B450 Pro.