depends what im doing if im honest. Mac's work in a very different way of course, or at least they used to. theyre very ram dependant rather than processor. I can be working with 32+ tracks of very high quality audio plus virtual instruments with no problem on the mac. Ive not actually tried such large scale productions on pc purely due to my external firewire 800 drive being mac formatted.
Once upon a time, I used to do all file format conversions on PC as I found powerpc architecture to be slower than intel for that, as with amd vs intel, but
now mac use intel, it's not an issue.
I did however start out using cubase on the PC before i bought my mac which I found didnt struggle at all and that was a similar spec. If it werent for apple's logic studio and my preference for the mac edition of pro tools, I would probably be back on a pc for that too rather than trying to justify the high price once more.
A large number of my colleagues have actually gone back to purpose built PC based machines.
There are a few editing suites, including industry standard Pyramix which only work on PCs
In short, personally, I find my mac is just excellent at what I want it to do. absolutely no doubt there, but my windows laptop is a brilliantly versatile machine on the flipside.
I would say that unless you're spending a lot of time processing large amounts of audio, or video, or doing high definition graphics (the screens on mac's are awesome), your money probably goes further on a PC.
Lets not forget aftersales. Apple have been very very good to me. some people have had more trouble. A successful house producer told me that he had been sold a 'slow g5' and apple wouldnt replace it, because aparently all macs are not born equal, or at least werent when the g5s came out.
but say your machine does break, there are a million and one guys out there who can fix any problem on a PC almost while you wait, with an apple, your downtime increases dramatically. Something ive seen in studios causing havoc.
Macs are awesome, I love mine, but Ive tried to be as detatched in my response as possible.