Thanks for the replies, they really help. The machine that I am considering, by the way, is a home built, not a stock machine. Sounds like I should stay with the 800MHz memory as stock. I did consider the 2.6 GHz CPU, but am really wondering if it is worth the 60% mark-up. Making the jump to the 2.4GHz also adds the 4MB L2 cache, so it should improve performance over the 2.2GHz (indepent of freq). I will make sure that the board can accept future quad or faster duals in the future... I can always roll the 2.4GHz to one of my other computers.
As for the Mac vs Windows decision... I am currently running an XP machine, but have had Mac's in the past. The main reason for switching back to Windows was software availability. It looks like Adobe has still not upgraded Photoshop to universal binary, so I would suspect some of the benefits of the faster Mac Pro are lost in the translation via Rosetta. Is this true? If so, then I do have a concern regarding Adobe's (and others) commitment to the mac platform. Not a slam regarding Adobe, since they truly make a great product, but nevertheless a concern when selecting a system for the long haul.
One other question... regarding Tived's comment on selecting an AMD processor. Can I ask why you are selecting an AMD over the Core 2's. Personally, I try to build with AMD processors. However, when researching on the TomsHardware site, I see that the comparison of the AMD vs Intel when running photoshop conversions, places the Core2's in the lead. I would appreciate your comments.
Thanks again.