AMD Phenom II x4 960T

no, your cpu is rated at 3ghz with 4 threads....most games will use 2 cores, some all 4....the 960t is actually made on a 6 core dye, on the right motherboard you can unlock the dormant cores...why did you need to ask that question do you see people saying they have a 12ghz computer?

Not really, no.
I just don't understand how it all works.

For instance, Deus Ex: Human Revolution's recommended specs call for an Phenom II quad core, but doesn't give a CPU speed.
So I don't know how the speed would be calculated on a game that calls for 4 cores.

Hi and welcome to Tom's forum.

The speed (frequency) that you see there is the frequency for each core BUT that doesn't means that you have 12GHz, that's not possible. All four cores runs at 3GHz and the entire CPU runs at the same speed.

Regarding the games, some games only use two cores and mostly of the current games only use three cores. In other words, your games use the cores that they need but the frequency is the same independent of the amount of cores that your games use.

So then, at the moment, quad-cores are basically only good for multitasking.

With the exception of games that make use of the 4 cores, thus making the game run more efficiently?

(Thanks for the welcome by the way  

Correct, even, a two cores at 2.8GHz can performs better that single core at 3.4GHz. The frequency is important but it's not all in CPUs. The games that use more cores runs much better because have more hardware for use.

So in a game that utilizes quad-cores, a quad-core at 3.0GHz would perform better then a dual core at 4.0GHz?

Correct