Two facts first:
- the amount of neccessary cpu time depends on the WU
- on the 1st page of the top hosts there are only 2 AMD systems and both use linux, where cpu usage is a lot higher -> this is not cpu-related

Doing a quick check I find the following:
4,971.51 credit WU (high cpu usage)
- i7 2850s
- C2Q 2500s
- Ph II 3025s

5,535.51 credit WU (low cpu usage)
- i7 550s
- C2Q 430s
- Ph II 680s

Note that the i7 and the P2 run stock GTX 295 (1.25 GHz), whereas the C2Q runs significantly OCed (1.51 GHz), so its CPU is working for a shorter amount of time. And most importantly: we can't know the clock speeds. At stock these CPUs are approximately comparable, but any of them could be clocked at least 30% higher, which would reduce the cpu seconds needed for the same task.

MrS
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Scanning for our furry friends since Jan 2002

BOINC doesn't show the real clock speed. One could try to guess it from benchmark values, but this is tough as it differs from version to version.

The Mars? Pretty uninteresting in my point of view. For gaming you could just as well get 2 285 for a fraction of the price and for GPU-Grid you could get about 3 295 for that money, which should be at least 2.5 times more productive.

MrS
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Scanning for our furry friends since Jan 2002