They are both good lenses, with polarization and 100% UV protection. The 580 in 580 lens refers to yellow bands of light. The 580 lens (their premium lens) is supposed to block more of the yellow shades (which they claim the eye has a hard time processing). This is especially important if you are tying to see better on water (like when sightfishing or sailing). The 580 is a glass lens that comes in gray, copper, blue and green mirrors. The Costa Del Mar website describes the recommended uses for each color. http://www.costadelmar.com/SeeOutThe...ensPerfection/ FWIW, I have two pairs of shades with the 580 lens and find that they are excellent for sightfishing and general use (although Kaenon sunglasses would be a close second).
I have the Stringers with the green mirror 400 glass lens. I think they are sweet but I have not worn the 580's. I had a hard time justifying paying the $200 that I did for them, let alone spending another $40 for the 580 lens. Maybe next time.