I don't think it's irrelevant as there is a bottle neck in any system. There'd be no point in pairing up the latest and greatest graphics card with only an average processor as it would hold you back. The graphics card is waiting on the processor to hurry up. The reverse scenario would also be true.
The point I was making is that you can have a 3Ghz processor and a 2.4Ghz processor.
The 2.4Ghz processor can easily outperform the 3Ghz processor on the basis it is simply a better processor in other areas.
As a real-world example, the Core 2 Duo 78200 has a clock speed of 2.53Ghz.
Yet it is better than a Core 2 Duo E6850 which has a clock speed of 3Ghz.
It's all very well having quad-core but if you don't do anything that needs quad-core you may as well throw your money down the drain.
Games of the future will make use of quad-core eventually. At the moment they don't. By the time mainstream games do we'll be on the (currently fictional but plausible) Core i15 series with DDR4 memory