Transeau said:
3.0 with 1G...
CPU's are $800+ each right now... if you go with 2.6 or 2.0, you could find yourself wanting more later... $1600 is a bit much post-purchase.
Memory is / will be cheap. I paid $545 for 5GB. (4x1G + 2x512M)
You can't simply look at the price per CPU. You have to look at the cost of the 2.66 in comparison to the 3.0
(prices from newegg.com)
Two 2.66Ghz CPUs right now would be: $1431
Two 3.0Ghz CPUs would be: $1734
A difference of roughly $300. If you look at the 2.0Ghz and the 2.66Ghz the difference is closer to the $800.
2.66 is the sweet spot. It has also been shown that the increase in performance between the 2.66 and the 3.0 is negligible.
Also, you wouldnt be spending $1600 post purchase if you consider you could see of the 2.66 CPUs.
The memory is cheap, but the 3.0 upgrade is a ripoff. It has been shown by anandtech that the chances of popping in a quad core later is likely.
So go for the best bang for your buck. Which would be the 2.66 stock, add after market RAM, sell 2x512MB and use your Mac Pro for a few years. If you feel like you need more oomph, i am sure the quad cores will be priced vry nicely and by then apps should be taking full advantage of that power. It will run like a brand new Mac.