Your site is testing incorrectly.
Finally, x264 encoding performance where you see 4.5ghz i5 6600k match a 9590 @5ghz
^This is often tested wrongly, because reviewers use a 5 year old encoder version with a popular benchmark that is terrible and doesn't show performance improvements that newer CPU's have from avx2 etc. This test is accurate.
and IPC gains of 11.9% over Haswell, 37.7% over sandy bridge
can we stop pretending that skylake is a disappointment? It's exactly what i expected plus a little more (was erring on the cynical side). There's no need for this drama on every new CPU release when tock to tock it's not all -that- bad, especially considering that you'll probably get ~5% more from clocking 200mhz higher than Haswell (especially non-DC)
Sure, it should be 6 core. It could be faster - but it's here and it's NOT slower than a 4790k.