Cinebench has no error checking and thus cant tell you if you are stable. A unstable overclock is one that causes errors. Sometimes this won't crash the program or windows install but will corrupt data and after a few days or weeks you will have a problem.
For example you copy lots of data from one hard disk to another and notice that many videos no long play because they are corrupted. Games will have strange bugs, saves will get rarely corrupted. Run a program to test stablity that has some form of error detection.
Will my 3800x it would appear stable in cinebench but restart the PC after 4 hours of memtest. The system would appear completely stable to me otherwise. Overclocking is fun, just be careful and test the cpu correctly after changing setings.
With a water cooling setup I had to do nothing for my 3800x to hit 4.4-4.45GHz in games.