There are two Semprons that run at 1600MHz on Socket 754 - one has 128KB of cache and the other has 256KB of cache. The one with 128KB of cache has a 2600+ rating and the other has a 2800+ rating, which is supposed to make it the equivalent of a 2.6 and 2.8GHz Pentium 4 respectively.
However, all processors have their strengths and weaknesses. You have to find out what they are so that the strengths match your computing needs.