Jon: you mean weaker yellow as in a different cutoff wavelength, or yellow with more magenta in it? My enlarger has dichroic filters and turning the knobs just winds the filters in/out. So "less yellow" just means more blue gets in - seems to me it would be the same as extending the magenta exposure. Using actual designed-for-multigrade filters could well be different, I don't know.
JBrunner: OK, I shall try that.