5D and 30D lenses

Come to think of it I don't think I've used the 50mm wide open since I got the 5d...

Tests on .the-digital-picture.com show the following results on a FF format with vignetting at the corners.

50mm f/1.4:
@ f/2.0, 1 stop
@ f/4.0, less than 1/2 stop
only at f/1.4 does it exceed 2 stops

50mm f/1.8
@ f/2.0, 2 stops
@ f/4.0, 1/2 stop

It would appear from these tests that the 50mm f/1.4 is less prone to vignetting than the 50mm f/1.8.