Before I consider mounting my ARCTIC Liquid Freezer II 240 to the pcu CPU, would the Arctic MX-4 paste be sufficient or does anyone else have any better recommendations ?
The MX-4 is definitely enough for nearly any use case.
But like MeanMachine41 mentioned, I would recommend Thermal Grizlly Kryonaut or at least Hydronaut if you have not already bought the MX-4. However to be completely honest Thermal Grizzly produces high end thermal pastes but you will probably not notice any difference if you are not fighting for every °C. Your CPU will run approximately 1-2 °C cooler with Kryonaut then with MX-4. Here is a recent video where someone tested different thermal pastes including Kyronaut and MX-4.
Kryonaut I'd advise caution with because it is a lower viscosity TIM and it can have enough pump out to require a repaste in a relatively short time. Something I experienced earlier this month.