I want to see Khan's chin tested first at 140. The improvements he's made under Roach are quite apparent but he's fought guys who really aren't that much of a danger to him, Barrera was really small and old, Kotelnik's style was made for him and Malignaggi really can't break an egg, it's not like Khan is a defensive wizard like Mayweather, he makes mistakes when he's on offense and it would only take 1 shot from Gatti to end it, I'm pretty sure Gatti would catch him, it just depends on how Khan reacts, but considering how big a puncher Gatti was, I'd lean towards saying Khan would not take it very well.
Gatti by come from behind KO.
seriously, khan is way higher skillwise. His hand speed would kill gatti in like 5-7 rounds, if it weren't for his crazy tough chin, it might even get stopped earlier by ref because he's taking to much punishment.