You should run stability tests and watch temps while they run, such as Prime95, OCCT, LinX, ect
You want to keep load temps under 70-75C if you can, ideally less of course, but if you want to push high frequencies you're going to be seeing 7x-80+ possibly. Once you start hitting 80C while load testing that's too hot, so you'll need to back off the voltage or frequency, or both, then try again a different way.
For 4.5Ghz, ya under or around 60C load should be doable if you have a good cooler, might get 65C or so depending on the voltages you use