I am looking for good liquid cooling for 70€ to handle 4.2ghz for safe temperature and volts but I dont know which will be perfect.
I wouldn't go less than a Corsair H80i.
Here are AMD Recommended CPU Coolers for Threadrippers: Thermal Solutions for Ryzen™ Threadripper™ Processors | AMD
The smaller the Rad the noisier/faster the fan(s) - 4.2? go with an 360 Rad hence 3 fans if you like it quiet under load.
Enermax liqmax 2 120s, cool's it superb. It does make some noise if you set it on medium level fan speed. Ideal temps are in 30-40°c with 20°c room temperature and under extreme heat setting with prime95 under 70°c, however keep in mind that GPU temps also comes into play. There is also nothing on the planet that will make such heat like prime95 does so,... I only have it set on medium speed via the switches it has on the fans, you can go up a notch but logically it will become louder.
It also has excelent reviews from tech websites, keep in mind it's a 120mm radiator,...