I haven't used one, but I think an upspiral bit will help a lot here.
With a groove this wide, you'll want multiple passes, I expect.
The router bit stops much more cleanly than the blades, if you don't want
the dado to go all the way across.
This is an area where the RAS really shines. The board stays still and
supported for cross dados and is easily guided along the fence for dados of
any length in the rip direction! You don't have to worry about the work