[LoRd_MuldeR]

If with "speed" you are referring purely to the clock frequency, then newer CPU models may not necessarily be "faster" (or can even be "slower") than older ones.

But: You have to keep in mind that clock frequency certainly isn't everything! Just think about the Pentium 4 disaster. In general, newer CPU architectures tend to be more efficient than older ones, in terms of "performance per clock cycle" as well as in terms of "performance per watt". So, it is indeed possible that a newer CPU may outperform and older CPU model at the same or even at a somewhat lower clock frequency - while also consuming less power.

Another thing to consider: There currently is a trend to stuff more and more CPU cores into a single CPU package. Those CPU models with a very high number of cores tend to have a lower clock frequency, compared to CPU models (of the same generation) that have fewer cores, because there is a power budget limit! Which one is better/worse depends a lot on which kind of application you are running. As long as your application is able to actually use all the CPU cores, I'd say the more CPU cores the better - even if it means a somewhat lower clock frequency. But, most applications have a limit on how many CPU cores they can use! So, in some scenarios, a model with fewer CPU cores but higher clock frequency can be better.

After all, you probably shouldn't fixate too much on clock frequency (and neither one the sheer number of CPU cores), but instead look for some actual benchmarking results of the particular application that you are planing to run.