At the risk of incurring the rath of the previous responders, No, what you
propose is not a good idea.

The basic idea of testing the film speed, zone testing, etc, with the filter
in place is fine.

Doing the testing in overcast daylight where the planned use is in studio,
under tungsten or electronic flash, is a bad idea because the color
temperature of overcast daylight is much higher than anything you will use
in the studio. The studio response of the film/filter combination will be
quite different than your testing experioence, rendering the point of your
testing largely irrelevant.

Thanks for this info. Please could you explain a bit more?

If I calculate the film speed and development time for N using my
outdoor results, will the difference indoors with electronic flash (or
tungsten) be so significantly different that the results will be
unusable, given that contrast can be controlled in the studio?

By how much would the color temperature outside differ from my
electronic flash, and by how much do you think it would throw out the
speed test & development time results on black & white film?

I suppose I could light the gray card indoors with an electronic
flash. Will it not matter that I shall subsequently use varied
lighting set-ups (and number of lights).

TIA

regards, phil lamerton