F100 is no problem with glasses at all . FM2n is known to give problems with people wearing glasses (my fm-10 is no problem).
I myself have -6.5 in both eyes, so I don't even bother buying the -3 diopters.

I suggest www.bythom.com

Thom Hogan is a true Nikon specialist. He wears glasses and has small hands. In his excellent reviews he always tells how the viewfinder works with glasses.
And besides he is also a fine photographer, so a highly recommended site (most other sites are very subjective, and the more technical sites are often by people not photographing).