I buy up lots of old B&W paper for lith printing. (Lith can give clean whites with fairly fogged paper).
I cut a thin strip from each pack, maybe 1/4" x 2", develop half of the strip in normal print developer, fix and wash and turn the light on. You'll get a sample of paper white and how much fog, on the same strip. Dry it, write the date on it, scotch tape it to the paper package. (I consider my good liht papers as precious and priceless, so i don't use whole sheets for testing - just a sliver will give you an idea.)