i'm in a similar boat. I think i'm going for the 8 core, but the 2.26.
Seems like way too much for the upgrade to 2.66.
Or, I may go used 2.8 or 3.2 8 core from 2008. Either way, it IS time to go Intel.
Although I might try to wait until January. If you can wait until then, the bugs will be out of snow leopard, and very likely the mac pro's could see a bump and a price shift. From what i understand, logic isn't super optimized for 8 cores YET, so YMMV. My biggest hope for logic and snow leopard though is the fact that the GPU's will be used at some point to do processing. At that point, I think your CPU becomes a little less critical.
Sorry, i think i may have added to your choices...