But what about a situtaion where you have independent threads? The the N core solution could be better than the 1 core.
Your standard consumer CPU is able to multi-task without any significant overhead. So you'd have equivalent performance.
Edit - I wasn't entirely correct. As N gets bigger this becomes less true. The overhead for switching tasks becomes more and more of a factor as N gets larger. At 4 threads you couldn't tell at all. At 40 threads, you might be able to tell a little (I'm not sure how much). With hundreds of threads, a single core would start to get bogged down. For you or I, though, the N gigahertz CPU would probably be optimal.
Edit edit: by "threads" I mean threads that will take up a significant portion of CPU time, such as a video application or a flash game, not the background tasks that you'll see if you open up the windows task manager. What's important isn't really the number of threads, but how often the CPU has to switch between them.