Russian, does this look like real world test conditions to you? Looks like an open air bench to me.
That's fine. I can link a lot of reviews that prove my point.
Akasa Venom Medusa vs. high-end AIO CLC in a case. The competing higher end AIO CLCs look like a waste of $ in comparison.
http://www.pcgameware.co.uk/reviews/cpu-coolers/akasa-venom-medusa-cpu-cooler-review/
That's a $50 air cooler.
Look at this, $60 Phanteks with a 6-core CPU using way more power than Skylake. No problems.
100-200mhz extra is the most realistic scenario for the $100-200 AIO CLC over a $45-60 air cooler; and that's assuming the CPU doesn't crap out at 4.6-4.7Ghz in the first place as not all i5 6600K CPUs can reach 4.8Ghz.
But he wants to buy an i5 6600K, not i7 6700K/upcoming i7 6800K or even the i7 5820K.
It's one thing to buy a liquid cooling system for flagship CPUs, and totally another on an i5. A max overclocked i7 6700K uses less than 200W of power.
I guarantee it that a
$20 Zalman CNPS14X will max out an i5 6600K @ 4.7Ghz without a sweat. It would be a cakewalk actually.
Even at only 800rpm, this $20 air cooler is enough to keep an i7 3960X @ 4.375Ghz.
i7 6700K + $20 Zalman CNPS14X >>>> i5 6600K with
any CPU cooler in the world.
In CPU limited games, even a stock i7 6700K will beat a max overclocked i5 6600K:
http://www.sweclockers.com/test/20862-intel-core-i7-6700k-och-i5-6600k-skylake/14#content
AIO CLCs have their place but in the OP's case, this isn't one of those situations.
As I mentioned before too, i7 6800K 6-core BW-E is launching in a matter of weeks. That CPU @ 4.5Ghz with that $20 Zalman heatsink is also a better choice to keep as a primary gaming system for 5+ years vs. a i5 6600K. In CPU limited sections of Fallout 4, Crysis 3, The Witcher 3 and Assassin's Creed Syndicate, etc. even a max overclocked i5 6600K approaches
90-95% CPU usage, leaving almost no headroom for future more demanding games. Why buy an i5 and an expensive cooling system when even a 4.6Ghz i5 6600K is nearly maxed out in some games? The part here that makes no sense is that running an i5 6600K OC at 40C or 90C makes no difference to its longevity or performance under real world conditions. That's what the companies trying to sell us $150-200 cooling systems don't want us to know. OTOH, there is a tangible benefits to a 4C HT i7 6700K or upcoming 6C i7 6800K for games where you are CPU limited (need higher minimum FPS).
Where AIO CLC or custom loop excels is the situation of overclocking 320W+ CPUs (X99 series) or in cases where you cannot fit the air cooler into a small case in the first place. Otherwise, air cooling wins hands down.