Multi-core Processors

In general, is a lower GHz multi-core processor better than a higher GHz single-core? Like is my 2.66 GHz quad-core processor better than the 3.1 GHz dual-core I was considering?

It depends. Essentially a multi-core chip is multiple processing cores on the same die. It will all depend on what you are doing. If you know your applications won't support quad it would be better to get a higher speed dual. If your applications do support quad core, you should try to get the best speed possible with 4 cores.

Another thing to take note of is the Turbo Boost feature on the newer Intel cpus as of 2010 and the new ones due in a few days. Turbo Boost turns off certain cores automatically so that the CPU can overclock itself. For example, if only one core is being used the other 3 will be disabled and core 0 will be overclocked. Same goes if you are only using 2 or 3 cores instead of all 4.

Another problem is programmers. Right now parallel programming isn't taught by default. Without programmers who can truly take advantage of multi-core we're still stuck as if we're all using single core machines. Things have gotten better but improvements could still be made to our operating systems to support multi core.

In short, do your research about what you're going to be doing. If it's only dual core, you could go for a higher clock dual. If it's quad try to get the best CPU you can for your budget. If you go the quad route just remember that you will be getting optimizations through Turbo Boost.