Photography: Camera sensor size difference

28mm is wide on a FF sensor (like a 5D)
50mm is a standard field of view on a FF sensor (like the 5D)

28mm is a standard field of view on a cropped sensor (like a 550D)
50mm is a slightly telephoto field of view on a cropped sensor (like the 550D)

If you are nice to me I can sling a 28mm and 50mm onto a 5D and 550D and shoot a picture later on if you want, might give you an idea.

Oh I know about the crop factor the only thing I'm wondering is whether a 28 will be wide enough for groups and landscapes.