Unless he's having trouble with weight this looks like a bad move on several fronts. First, I think he struggles at 154, he seems like an average size welter and would lose some of his better attributes by fighting bigger men. Margartio and Clottey are the size of guys he'll be in with and he struggeld in those bouts. Second, 154 lacks the big names that welterweight has. Cotto won't be around much longer and the big paydays are at welterweight he should get in on them now. Having said that I still think he beats Foreman.
Outside of Martinez I think he could beat almost anyone, possibly including Williams. Cotto has a lot of trouble with speed, overall.