Lets just say that C2E is : 75% costlier for about maybe 30-40% performance increase as compared to its nearest rival.
that said, since there is 'technically' no price limit involved - why would you not want the best ?
for ur question as to: is the processor the limiting factor: answer in one word No.
sure you need a lot of things + good programming to get the best out of your hardware.
lets just say that a processor performs operations on operands (data) - so ur data bus/channels need to be just as fast and u need a lot of memory at each level...
the C2E has 12 MB cache - which i'd say should suffice the processors requirement. get some exorbitant amount of ram (16gb) with low latency and high bus speeds - i'm guessing that the basic bottle necks are taken care off.
beyond that on secondary storage -get a good SSD+HDD over a SATA + fiber channel ; thats good stuff!

these are good spec's if you are into the whole virtualization thing and want to run your guest systems at break neck speeds.