I've created this site to distribute optimized SETI and BOINC clients. These clients are the product of optimizations that many people have done. The most important contributions have been made by Tetsuji Maverick Rai, Alex Kan, and Hans Dorn. I did some, too. The SETI client runs faster than any other client I'm aware of, and it will give results that are strongly similar to the official client. This is BOINC jargon for identical.
If you are interested in whether a particular workunit will be validated, which they all should, you can run it with an official client and with my client, and then compare the results using sah_validate, a program which I wrote for this purpose. However, I personally use Tetsuji's excellent rescmp, because it tells you whether the similarity is strong or weak.
The sources are available from a subversion repository, although most people should just download the executables.
Changes to Berkeley's code: