having read the posts on Canon lens variation for some time, i decided to order 2 lenses and keep the best - at least giving a reasonable probability of avoiding a bad lens with low probability of getting a great lens
so i tested two 50mm 1.4 lenses on my 5D and new 40D - and one was noticeably better. wide open, it was sharper overall, with noticeably better corners on the 5D up to 5.6 (couldn't tell a difference at f8).
corners were better with the 40D on both lenses than the 5D (not too surprising), but still noticebly better to f4 with the "better" lens
on the 40D, both 50 1.4s were better than the 17-85 at f5.6
on the 5D, the 24-105 was as good as the 50 1.4 at f4
hopefully not everyone will read this post and "cherry pick" the lenses so next time i have to order 10 to get a good one