Are stainless valves harder on stock iron head seats?

I looked through hardness numbers for both they are not far apart. As indicated above in a couple of posts, the normal use of hardness numbers (removal of one substance by another in a rubbing or grinding motion) is not really the issue, especially if the valve set up is not rotating the valves which was done to keep lead from building excessive lead oxide deposits on older engine designs.

IMHO, it is matters like the heat levels and softening of the seat that are the issues. The transfer of material idea above is a pretty interesting observation too. Plus in a performance engine, controlling the valves well with the spring selection to avoid valve bounce seems like it would be critical.