Xeon is honestly a really bad option, not just because it is an old and overpriced CPU but also because After Effects is not Multithreaded "yet", and even when it will, it won't be multithreaded in the live preview etc - just rendering. You will notice a significant drop in responsiveness in the software compared to pretty much every other CPUs while working - and frankly it's not worth the money! If you are forced to xeon because you are on a mac, you would notice faster responsiveness in After effects on a regular 27 inch iMac than a Mac Pro with Xeon processors, for a fraction of the cost (there's a reason why Apple is Phasing out Intel more and more with every hardware update). If you are on a PC, you should seriously NOT buy a Xeon, now that AMD has released high core/high speed CPUs. Intel is "dead" until they can match Apple and AMDs nanometer sizes - and I have experienced the difference first hand and can tell you you will feel ripped off.
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