I think when Chavez fills out and hits his prime he will be fighting at 154 or 160. He is about 6'0 tall and I think Boxrec has his height listed incorrectly. I dont see Amir Khan filling out as much as Chavez. Amir looks as if he has already filled out and is extremely toned and muscular. Chavez still lacks this and appears skinny and fragile at 147lbs. I haven't seen an Amir fight yet just highlight clips and individual rounds but not a fight. I just dont think Amir is big enough to fill into a superwelter or middle weight so I doubt they would meet.
There are way too many questions about Khan that have not been answered. Although Khan may have more amatuer experience, the professional level is different. JCC has the upper hand right now, due to his exposure in the pros.