Hmm... well the whole point of having a Xeon processor is to get multiprocessor support. Unless the Xeon has a faster FSB than the standard Core 2 Quad, then I would go for the PC.
Another thing I would look at is the RAM latency. Apple uses FB-DIMMs with ECC, which is slower than standard non-ECC RAM, and the extra buffering increases memory latency in exchange for more capacity. If you don't need large amounts of RAM, then the PC would win, assuming that you use RAM that is as fast as or faster than the Mac Pro.
However, if you are doing critical stuff on the computer and the world would end if the RAM got a very unlikely error, then the Mac Pro would win since it has ECC. Keep in mind that ECC RAM also costs a lot more than standard RAM, and FB-DIMM ECC RAM costs even more.
As for the other stuff, I would go for the PC. If I were building the system, I would build a RAID array with two 10K or 15K hard drives for extra OS performance and another array with larger standard speed drives for storage. Not sure if it would cost the same though...
Anyways, I'm more inclined to go with the PC, since its easier to upgrade. Apple I think needs Apple versions of otherwise standard hardware which cost much more without any difference other than it works with a Mac. (This may not be true anymore, I don't know).
As for OS security, I would go with Vista. By itself its extremely insecure, but with a bit of tinkering and a few addons (that may or may not cost large sums of money), it should be secure enough. Mac OS X has its own security flaws, such as a firewall thats not on by default (maybe its fixed) and updates that don't announce themselves as security related (Quicktime exploit).
I would go with the PC, but thats just me.
C. P. U. Its not a big processor... Its a series of pipes!
Last edited by The Architect; 14-01-2008 at 10:26 AM.