Go with the 2.93 quad if you mostly use single threaded apps and want applications like Photoshop to be the fastest they can be. However, you also have to take into consideration the 8GB RAM limit (and 4GB sticks are out of the question due to their high price).
Go with the 2.26 octo if you need more raw power for encoding video faster, or using more apps simultaneously, or if you need more plugins in Logic etc.
I have the same dilemma as you, as I want my machine to be super fast in every situation and also being able to take 16GB of RAM. But I'm not paying $5000+ for a bare computer.
It will be interesting to see how the 2.26 octo with 16GB RAM compares to the 2.93 quad with 8GB of RAM with single threaded apps. If the difference is not too great, I'll go with the 2.26 octo and give it 16GB of RAM. If not, I'll take the quad.