As long as you don't put in 50mm spacers or any such foolish thing you'll be all right, 20mm is not an exaggeration and even though it will put some strain, it's nothing the car cannot take. I have friends who've had them on for three, four years now and they never had a
problem. The important thing is that they're good quality, and as for everything else, the specific ones ( 5x100) are better than the generic ones.