I want to buy an i5 8600k and overclock it to 5.0ghz at least. I want to know if I need a watercooling or if I can use an air cooling system. I also want to know if you could tell me if there is a big difference between a 120mm radiator and a 240mm one for this kind of overclock.
Some people go fan only but not me.
The 240 may cost more the the 80 but the 240 would allow the water more time to cool in more radiator.
Seeing how you are looking for 5g
I would recommend the 240 to 280 if your case can handle it.
Better to have more cooling the not enouuh.
I have corsair h100i 2x120mm = 240mm on a fx 6300,
A h110i 2x140mm =280mm on a fx 8350, and h110i on a ryzen 5 2600x all 3 set up top and fans as exhaust.
The 8350 is oc'd for a safe 24/7 at 4.5ghz running a prime95 small fft's stress test temps stay 50-60c in The the heat of the summer in a room that doesn't get air conditioning to it.
The ryzen running same tests runs 76c with percission boost overdrive and extended frequency range2 enabled.
Hope this helps.
Well with that aim not 120mm for sure. General rule of the thumb is that cheap water cooling is worse than good air and 120mm ones are all cheap.
So either get 240mm one OR really high end air cooler, which are surprisingly good actually - something like 80 bucks air cooler would do better than any 120mm cooler and probably some crappy 240mm ones too.