17-40mm is best used from 20mm and above and the corners are not that bad.... below 20mm, it is bad... but you buy a UWA for FF, and if 17-20mm corner is not sharp.. it could be an issue for some..... but on APS sensor.... I think it is still ok....... 17-40mm was my main lens till I got 17-55mm......
Do note that when you rent lens, lens variation does exist too......
gonna use the 17-40L on 5DMK3.
currently on 10-22 + 17-55 with 7D.
i'm not after super sharp photos, i'm cool as long as the 17-40L performs similar to my 10-22 at widest focal length.
yeah i know IQ may varies but i guess will not have too big a difference?