In theory, the higher the ratings gap, the more points will "change hands". If a 1650 faces a 1680 and wins, the 1650 will gain many points and the 1680 will lose many. If the 1680 wins, he will win a few points, and the 1650 will lose a few points.
However, in reality, it isn't as simple as this. I've certainly played games for example against people with a rating 10 points lower and gained 25 points from winning. There must be other factors, but I do not know what they are.
Take my love, take my land, take me where I cannot stand.
I don't care, I'm still free, you can't take the sky from me.
Take me out to the black, tell them I ain't comin' back.
Burn the land and boil the sea, you can't take the sky from me.
There's no place I can be, since I found Serenity.
But you can't take the sky from me...