Total mismatch. Starling by stoppage anytime he chooses to step on the gas. There's LITERALLY hundreds of welterweights in history who would beat Khan.
Above 140, I don't think you have to be a big puncher to stop Khan. Chris Algeri was hurting Khan for Christ sake. Khan's speed and length don't do him much good because his defense is terrible. Starling would walk through him.
Starling wrecks him. Khan's speed gives him an early advantage but Starling's counters to the head and body take the fight out of him and he gets stopped in the middle rounds.