Higher processor clock speed will render faster.  More cores (and HyperThreading) will multiply render speed.  More memory gives greater capacity;  i.e., you can render more complex scenes at better quality settings and larger pixel dimensions.  More memory will render faster than less memory if Firefly approaches the lesser memory's limit.

     In general, get more cores (and a HyperThreaded quad is roughly equal to seven cores*), with a secondary emphasis on clock speed (3.2 GHz is better than 2.4 GHz).  But having chosen more cores, now you need to get more RAM to feed all the extra cores.  I would get as much RAM as you can afford and the motherboard will hold.

     A HyperThreaded quad core i7 with 12 GB of RAM is a great balance of price and power nowadays.  Any more, for 3D use, I simply wouldn't bother buying a computer which was not 64bit.

 

*  While you would render eight threads on a HyperThreaded quad, the HyperThreads only run at about 3/4 the speed of the primary core threads.  So, speed-wise, a H/T quad is about equal in speed to a hypothetical seven-core processor.

Poser 12, in feet.  

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