The P size will vignette unless you cut down the holder, but in doing so, you lose the ability to stack filters unless you handhold. The Z holder will vignette on the 5D/17-40L combo (I had one, sold it for this reason). I switched the holder to the Lee brand...no vignetting on the 5D/17-40L, even with all three filter slots in place (however, you will need the Lee 77mm wide angle adapter ring). For the money (holder is $15 more than the Z-Pro), you'd be better off with the Lee, and you won't have the constraints of the P-system. For the 5D, I'd definitely recommend the larger sized holder, first choice Lee, then Z-Pro.