Higher Frequence requires higher Voltage, or you will find the PC cannot boot or the applications will close automatically, especially games.
But higher Voltage will cause higher Temperature. If the Temperature is too high, it will cause errors in RAM, and applications will crash, games will freeze. Sometimes the PC will shutdown.
In summer, the indoor Temperature is higher, we must watch out.
If you don’t install extras fans to ventilate the air from the rear to the front, you should not set Frequency and Voltage too high.
So you should make sure the balance between Frequency and Voltage. You can look for some guides about your RAM models online. But you must set and test by yourself.
While playing games, almost every parts of PC works at best and the Temperature is up to its highest. So don’t trust those posts which only works as normal conditions, unless you don’t play any 3A games. The best way to test RAM is playing games, especially 3A or MMO, like Dota2 and CSGO.
CAS is positive correlation to Frequence, so don’t set CAS too low. But the lower CAS, the lower latency. It’s up to you, but most DDR4 RAMs can only get 16 as CAS at best.