Regarding rated speeds for film, I think there is a "standard" developer used for the official ISO speed test. It might be mentioned in the BTZS book, or the Film Developing Cookbook. As a few others have mentioned, I think the developer will have more of an impact on speed than meters.

I have read that the thin negatives are preferred, since for the same end result there is less light scattering by the silver grains (I can't remember the technical name for that).