Apple tries to stay away from MHz debates by promoting their work as more efficient and thereby faster by virtue better engineering, not raw MHz.
That being said, now that Mac has gone unix-like core, I think they are roughly equal to all the other systems out there.
Apple prides itself on first-rate manufacturing. This can be an obvious difference compared to the cut-rate prices on lower quality generic hardware. With better fit and finish on higher echelon PC brands, the price and quality difference can be less. I think a discerning home-builder can make something of adequate quality for a considerably less amount of money when not speaking of laptops.
The choice of Mac vs PC should be based more on your needs. Choosing Mac OS has long-term implications that you may not be willing to deal with. Once you choose your platform, you can shop for price vs performance with consideration of your impression of the quality of the brand.