Processors are usually compared using benchmarks. Software testing programs that record a speed comparison. Also when talking about Semprons, there are several versions that use different sockets, socket A, socket 754 and AM2, that I know of. They are all going to benchmark differently.
Here is an article from Tom's Hardware that is pretty comprehensive. It is 28 pages long. I guess the article doesn't go up to the new chips that use the AM2 socket.
http://www.tomshardware.com/2004/12/...t_2/index.html