If it was me, the 5820K would be my choice mostly because of the following:
1: 2 More cores (4 threads total)
2: The Haswell architecture maxes out most games already well below 4ghz
3: The Skylake has less PCIE lanes than Haswell-E (I know they have more this time but its still less unless I missed something)
4: Your going to get more distance in games in the future even with lets say 10% less on a clock to clock basis with the extra cores.
5: More room for expansion on the motherboard (X99 vs Z170)
That is my opinion of course!
1. 2 more cores are pointless if they are not used. Modern games do not show any benefit going from 4 to 6 Intel cores, none at all.
2. No it doesn't. There are plenty of CPU bound games - WoW (and other MMO's), Arma3 to name just two.
3. A 5820k can't run two GPU's in x16 x16 mode, only a 5930k or 5960x can, so Skylake is identical to a 5920k for 2 GPU uses in terms of PCI-E lanes. Skylake can also support a 4X PCI-E SSD from the Z170 chipset, thanks to DMI 3.0.
4. Do you really believe game developers will dedicate resources to make games perform better on 6+core intel CPU's, when less than 1% of the PC gamer userbase has a 6+ core CPU? The answer is no - they develop for the mainstream, not for the enthusiast.
5. This is only a benefit if the user is planning on 4 way crossfire/SLI, in which case he needs a 5930k or a 5960x to actually run 4 GPU's well, as a 5820k doesn't have enough lanes to do so (neither does Skylake).
