In your opinion who beats Khan at 140 and why?

[Weebler I]

I think Khan would destroy Marquez at 140, he just wouldnt be quick enough to keep up with him

I don't know about that, you don't need to be super-fast if you have great timing, and Marquez has already shown v Pacquiao (of all people) that his timing is impeccable. He's getting old however, so if the fight is to be made then it needs to be made soon.