Just to clarify:
I did't want to start a new edition of the filter vs no filter dispute. I fall into the have-clear-filter-on-always camp. I never noticed any image quality issues with or without. I'm sure there is a way to prove that another layer of glass does something but I don't care and want the additional protection.
SO when I'm asking about putting a polarizer or ND filter on top of the clear filter I'm only concerned about vignetting and when that kicks in. Adding a filter and taking it off again is quick and easy. Handling two filters out in the field makes me uncomfortable - even though I have to do it for my wide angle shots when I need a polarizer. It does vignette on 24mm that much I know and it's pretty obvious. With 50mm I just don't know.
I don't know of any tabulated results anywhere, I think you just have to test for yourself.
Some time back, I did so for the 24-105L, 16-35L II, 35L, and 85L II on FF, and the 17-55 on APS-C.
If it's any consolation, while the zooms had increased vignetting with stacked filters, the primes really didn't - the 35L could take 3 stacked F-Pro filters with no increase in vignetting and the 85L II had no increase with 2 F-Pro and a pretty insignificant increase with the 3rd.
Hope that helps...