Wouldn\'t it be worth building optimised clients for specific platforms (Athlon etc.)?

This comes up every few weeks.
If you use the search facility for \"optimised\", you can read the many posts on the subject.

The latest Windows sulphur client is highly optimized for both Intel and AMD. The only way to go faster at present is to go 64bit for those Intel and AMD PCs capable of that. That may be a ways off.

Edit...Unless you mean optimizing BOINC software itself, rather than the science app. If so, optimizing BOINC for specific platforms only affects the periodic benchmark results, not the speed with which the science app works.