I dont really think its a great time to be dropping $200 on a cpu if you are just planning to mine Primecoin.

On my intel i7 at ypool I am making about $2 a day before electricity (its my work computer so its always on anyway).  So it would take about 100 days to make ROI but with the recent developments in GPU mining progressing nicely, it seems CPU mining may be blown out of the water long before then.  Of course we may yet discover that GPU mining isnt much more efficient all-in-all but it is certainly something to consider before spending on new hardware.