I was talking to Tim, and the difference is really for the woods, IV for maple capped and harder, V for mahogany, but he can really tell you best.
On the Les Paul, the IV's are great. I like the balance of all IV's. Think of them as Mules with more kick
You can push the amp really nicely but still hear all the strings. Also, when you take the volume down, the IV has the best clean tones.
