Photoshop needs Rosetta right now. While its true that Rosetta eats RAM for breakfast, it needs raw processor speed more since its emulating another processor. The 2.0Ghz machine is bad value for money imo.
The 2.0Ghz machine costs $2199
The 2.66Ghz machine costs $2499
The 3.0Ghz machine costs $3299
The 2.66Ghz machine is 13.6% more expensive than the 2.0Ghz machine but has 33% faster processors.
The 3.0Ghz machine is 32.0% more expensive than the 2.66Ghz machine but has 12.8% faster processors.
Or put another way, the bank for buck is:
$274.87 per Ghz for the 2.0Ghz machine
$234.87 per Ghz for the 2.66Ghz machine
$274.92 per Ghz for the 3.0Ghz machine
The 2.0Ghz model has 8GHz of 'raw processing power'
The 2.66Ghz model has 10.64Ghz of 'raw processing power'
The 3.0Ghz model has 12Ghz of 'raw processing power'
Its pretty obvious imo that 90% of people looking to buy a Mac Pro should go for the 2.66Ghz model. The few that really need the extra power will go for the more expensive one and the few that need to save the pennies and need the extra storage space in the low end Mac Pro vs the 24" iMac will go for the 2.0Ghz model. The 2.66Ghz machine is clearly the best value for money machine, followed by the 3.0Ghz machine and the 2.0Ghz machine comes in bottom in terms of value for money since unlike the 3.0Ghz model, it starts to compete with the iMac 24".