How do you compare single and dual cores power

This may have a painfully obvious answer but here's the question:

My previous understanding:
I thought that having a dual-core processor is sort of like having two separate "minds" to work on your computer's tasks. So a 2.0 ghz dual-core will let you do two really hard tasks simultaneously, like watch a video while burning a CD. But for any one program, you have a maximum of 2.0 ghz brought to bear.

Single-core PC's with "hyper threading" are designed to try to multi-task better, so you can do two easy tasks simultaneously. It won't work as well as a dual-core but it will be cheaper.

Quad cores are like dual cores but more so - more multitasking power, but for more money and heat output.

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Crysis' system requirements are:

Quote:

CPU: Intel Pentium 4 2.8 GHz (3.2 GHz for Vista), Intel Core 2.0 GHz (2.2 GHz for Vista), AMD Athlon 2800+ (3200+ for Vista) or better

Now according to this, having a dual-core 2.0 Ghz allows your computer to do a task that would require a single-core 2.8 Ghz.

My question is, will 2.0 dual = 2.8 single for ALL applications, or only certain programs that are designed to take advantage of dual cores? Will 2.0 dual = XX single, where XX depends on the particular program? Is there some chart or formula you can use as a guide? And how do you compare quads to duals and singles?

It seems like within a year or two games will require 3.0 Ghz+. So will a 2.4 dual core handle that? A 2.8 dual? Do I have to go to a 3.0 dual to be on the safe side?

It's confusing. Thanks.

Jam it back in, in the dark.

That's what I suspected and was afraid of. Thanks.

There's nowhere I can't reach.