The Intel i7-5820K is a high end 22nm Haswell-E based 3.6 GHz 6-core CPU. It is in Intel's K line and so is unlocked allowing for easy overclocking. It fits with the LGA 2011 socket for motherboards that feature it.
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Pro Top performance in its price range
Tested against similar priced CPUs the 5820 edges out just about any other $400 CPU in 3DMark scores. While this may not translate to real world use at all times, this is a very high end CPU that will deliver for the money.
The Core i7 5820K is more expensive than similar i7 processor from the Skylake generation.