I think Khan is taking on too much this Saturday fighting at 155 when he's not long established as a welter-weight. He's looked much slower in his workouts. Any other examples of when boxers moved up too much and were out of there depth? Cleverly struggled at Cruiser vs Bellew II - all that extra weight gassed him out and he had a great engine at 175.
If Khan fought Lara at 154, the step up in weight would be far less significant. The problem with this fight is that he will face a cruiserweight on fight night.
There's a difference in size and mass. There's very little size difference between Mike Tyson and Victor Postol too.
Manny Pacquiao. He had no business at 140, 147, and LMW 150, but he defied logic and proved himself one of the GOATs of boxing history. Oscar De La Hoya at 160.