There are two different situations that we can consider:
- One kind of processor that is just used for calculations for a single program.
In this situation, the Processor speed is more important as the user want the ability to do quickly and efficiently. Its not the case with web server.
- On the other hand the processor used for multiple programs running at the same time. ( concurrent processes)
The second is where multiple cores come in handy, as each program can be assigned to a separate core, thus freeing each program from 'bottle-necking' each other.
- From Intel :)
Software developers can no longer rely on increasing clock speeds alone to speed up single-threaded applications; instead, to gain a competitive advantage, developers must learn how to properly design their applications to run in a threaded environment. Multi-core architectures have a single processor package that contains two or more processor "execution cores," or computational engines, and deliver—with appropriate software—fully parallel execution of multiple software threads.
- In my opinion
Multi-core processors are good for multi-tasking and High speed processors are good for high performance applications. Most high performance applications, like 3D rendering and gaming, will eat up all the CPU power.
So you would need as many cores AND as much speed as possible.
Hope this explanation helps.