The 5820K is a great chip and will see you well. For reference, I have a 3930K still that I have had since new back in 2011 and it still copes with everything hence me not changing it out. The drawback to the 5820K is the amount of lanes which could cause a problem if going more than 2 GPUs but other than that, it is a solid chip and will last for years.
As we move forward to DX12, I expect more games to support more cores, so I would be a little apprehensive of the 4C8T CPUs and look for more cores personally.