Okay, near as I can figure...
Using household tungsten lighting as the sole light source, Ilford MCIII RC paper can be rated at about ISO 3. ISO 2 if shadow detail is required.
This was the setup I used to arrive at this conclusion:
On a black cloth background, I set up an 18% gray card and a sheet of white paper. I aimed a 60-watt tungsten light bulb in a bowl reflector at it at a range of about two feet (60 cm). Incident light meter set at ISO 6 indicated an exposure of 1/8 seconds at f/2.8. I verified this with my SLR's TTL meter on the gray card. I shot five exposures, all at f/2.8: 1/8", 1/4", 1/2", 1/15", and 1/30". The exposure at 1/4" showed a nice density for the gray card, and at 1/2", the black background was beginning to show.
I processed the paper is Dektol 1+4 for 90 seconds at 75 degrees F (24 dec C). Normally, I use Dektol 1+5 for 120 seconds, but I elected to use my standard print process this time. At some point in the future, after I've established good baselines, I'll vary dilutions and development times.
Not the most scientific of tests, but I lack a densiometer, so it'll have to do. It should be accurate enough for general usage. Tomorrow, I'll spool up some more and run the same test outside in the sunlight. After that, I'll run the same set of tests using VC filters to check out contrast variations, since this is VC paper.
So, this can serve as a starting point for those interested in this process.