Tszyu might be too big, but if Rosario can manage 140 effectively he has the tools to knock out Kostya in a great one.
Rosario has a puncher's chance but Tszyu was quite durable... Vince Phillips had to hit him a lot to finally get rid of him... I don't see him as a guy likely to get stopped early in a fight... I think Rosario hurts him early but gets stopped himself mid rounds