Not like I'm providing new, surprising info or anything. But I figure that this has to be said. :/
Anyone who is past 60, can start leveing their NPC friend here. It's excellent, and the mobs are easy. The Desert Dhalmel strikes me as especially easy for its size, and it doesn't hit that hard either (in my opinion). Of course, mages may have a hard time due to its Silence attack, but bring some Echo Drops to fix that.
If the levels are correct, your fellowship partner could reasonably go to 42-43 without dropping off too far in the EXP-to-kill ratio.