Rios by KO at both 135, and 140. I'd probably take Khan't by decision at welter. Rios is a slug punching bag at 147.
This....Khan chin(Terrible, Bad or Average) will always be a liability.....unless his fighting dudes with pillows in their hands(Malignaggi, Alexander, Molina, Collazo, etc) with guys with some power he would be getting hurt, drop, or running for his life late in the fight.... Rios might be slow ass fuck....but he will keep coming...
I was going to post the exact same MM as it happens, Amir "AK Lord of Bolton" Vs Brandon "Punching bag Bro" Rios. It's an interesting matchup actually, very contrasting styles and strengths. I tend to think punching bag Bro wins at 135, 140 a pick em, and AK Lord of Bolton wins at 147.
At 135 and 140, Rios breaks him down and stops him late. Khan would have no way of keeping him from getting inside and Rios would have his way. Khan would start fast and get out to an early lead on the cards but by the mid rounds Rios would start to close the distance and make it an inside fight and Khan has no answer for that as he proved against Lamont Peterson. At 147, probably Khan but I can't really base it on anything other than Rios is no welterweight.