Ya what Mike said. I just wanted to ass that Intel CPUs with Hyper Threading a.k.a. HT (
info Link) allows a CPU core to process two threads at once. In general terms for crunching this works well but overall productions depends on the projects app and how well it is coded for optimization. Sloppy code works well with HT. For apps that are highly optimized for efficiency, it is recommended that the user disable HT in system BIOS to prevent the system from bogging down.
Personally I always have HT enabled on my two i7 boxes. Simply because its just a pain in the butt to keep enabling/disabling HT except for specific events like PrimeGrid Challenges. Although for the current challenge I forgot.
One other thing to note. Most projects, if not all, have a preference for a particular CPU brand as well as Operating System. This is dependent on how the app was coded as well as what type of work the app does. Though I do not keep track of such preferences, some of the Team Gurus like trigggl, zombie67, JPM and others are quite knowledgeable on such matters.