Somebody correct me if I've off base, but the Clayton kits don't include shocks or shock extensions, so either of those would be needed adding to the cost. Which is something the Rancho kits do come with, just something to keep in mind.
I’m running the same tire at 315/70/17 at 30 psi. Seems like a good spot, but the chalk test like Ddays mentioned will let you know specifically depending on how you’re running, heavy or light.