Fixed grade paper will only be blue sensitive. MG will be blue and green. I got some fair looking not-too-harsh contrast by shooting MGIV RC with a #8 filter, at EI 3 (not counting any filter factor - IOW I metered for EI 3 and just slapped the filter on and shot.) EI 6 was too think. 3 looks about right but something even a bit slower might be a touch better.