I would not send them for fog testing. When you send for fog testing, they will either pass or not pass very narrow definitions. And if it doest pass, they normally just throw it away. And just because it won't pass, doesn't mean you can't shoot on it. I've shot many, many times on film that not only was expired, but that the lab condemned.
Trick is to overexpose. Thankfully film can take a lot of over-exposure and still be fine. I would start with at least 1 stop overexposure for any expired film. Then the general rule is add 1 stop for each decade of expiration. Obviously, you will reach a point where the stock might be too old, where the radiation all around has has built up the fog levels too much.
Here's a good article from a stills magazine on subject: