I think that the Sls have a more concave look to them, even though it's subtle I notice it. Also the bends on the spokes on the Sls seem to be more rounded where the forged ones seem "sharper". I know that they're minor differences, but when putting down the money for wheels it's nice to get what you want
I'd be happy with either set, as long as I can get the set up I like. And I'm one of those people where no center cap bothers me