Everything I have read and seen says 2 1/4 hp is plenty so long as you are not doing a lot of them (e.g., in a production line). Assuming the proper profile, you can take multiple passes if you need to do so.
I saw a setup where the router bit was centered to the fence and two plastic pieces were clamped to the fence with part of the bit profile sticking through. With both pieces of plastic clamped to the fence, only 1/3 of the bit was showing. The panel was run against this setup, and then the first piece of plastic was removed revealing 2/3 of the bit. The panel was run against it, and then that piece of plastic was removed revealing the full profile of the bit for the final pass.