Yep, I think you're guessing right.
I think either will do it. For safety I'd choose Mules, but in some ways I'd lean towards Riff Raff out of the two based on my guitars. The Riff Raffs give me a tighter, more focused sound (not that the Mules are un-focused themselves :lol:). It all depends on what guitar it's going in. If it's already quite bright sounding, the Riff Raffs might seem a bit too cutting most of the time and could sound like they haven't got enough body on stuff played like that. To my ears, the Mules have a "raunchiness" in the mids that would fill it out.
Both would be very close though, I don't think I'd go for anything hotter myself.
Oh, and welcome to the forum! :D