RA4 papers are relatively "fast", optimized for automated printing. I worked for a number of years in the commercial lab business where we printed formats from 35mm through 8x10 color negatives. Given the size of our final prints, ranging from 8x10 to wall-mural sizes, there was never a need, I recall, for any ND filters as the exposures were plenty long to allow burn or dodge manipulation. We used dichroic heads from Durst or Omega with halogen lamps, sometimes as many as eight of them in a single head. As mentioned, it was customary to leave C filtration at 0, color correct with M and Y, and choose a functional aperture and time. I recall mural exposures over 12 feet in one direction, with exposure times in the 2-minute range. Lotsa blown bulbs and wasted material! That type of thing is done with large format inkjet these days.