I have read numerous forum posts that point to a 12 core being better for use with Cinema, however I've seen that the 6 core is ultimately faster....maybe.
What's the truth on this? I can only swing the 2.66ghz 12 core if I had to, the 2.93ghz is too much. The 6 cores are around the same price as the 2.66ghz 12 core but I understand that the 6 cores are 3.33ghz in speed.
It seems that the 12 cores are better due to the amount of cores, hence quicker rendering speed.
Which way you should go depends a lot on the type of work you do. If you're doing relatively simple scenes and not having problems with slow editor performance you should probably go for more more cores.
OTOH, if you're doing heavy stuff like character animation or lots of simulation, you may want to emphasize higher GHz over more cores, as most editor stuff doesn't benefit from multithreading.
Another thing to consider, if you're on the PC and don't mind a little DIY, is overclocking. The new Intel i7 chips are easy to overclock and can give you much more bang for your buck than Xeons.