Very simple. 64 bit OS / Client computers always overclaim. BOINC benchmarks is 64 bit in your case when all the work that WCG sends out is 32 bits and processed at 32 bit.

Actually, not always. That depends on the Boinc version used. Some are close to reality: although higher than the 32-bit benchmark they are more or less consistent with the work done which is generally a little higher with 64-bit systems.

But some versions of Boinc have a really weird 64-bit benchmark where the integer figure is 50 % higher than with the other versions under the very same conditions. This is unfortunately the case for the official version currently delivered with Ubuntu 9.04, and probably too for Macs according to your post.

Another reason for consistent overclaiming whatever the Boinc version or the operating system is that the benchmark does not behave correctly with hyperthreading, which is the case of i7 and P4HT processors. Under these conditions the benchmark (per virtual CPU) is the same as (or very close to) what it is when running only one task per physical core. Then, obviously, the claims are exaggerated and the granted credits tend to be much reduced to match the actual work done (more or lsss).

Cheers. Jean.