You think Roach won't account for that? Khan isn't a bum and won't be taken out so easily. Plus Floyd isn't a spring chicken anymore, he can't just counter Khan's speed that easily without tasting some leather. He will alter his strategy to counter Khan's speed and jab. I can see Floyd raising his game and showing his full arsenal to take Khan out. I don't see Floyd sitting back for Khan.
Khan would get schooled and embarrassed and knocked out faster than Ortiz did. That brittle Glass Jaw would get shattered everywhere.
A very slim chance, especially if it takes place in May 2012. I'll give Khan about a 5-10% chance of winning. Khan is physical gifted, but Floyd is leaps and bounds ahead of him in terms of ring intelligence, skills, and versatility.
Khan fast straight punches will give these US fighters problems, just like Paulie and Zab who could not adapt to Khan's speed and style of punches. Floyd will also find it hard to adjust, Khan improving timing and faster hand speed and jab will give Floyd NEW Problems something he has never seen.