Each CPU is different, so its really gonna be hard to give a recommendation, Its something you will have to play with, you can play with the EDC, TDC and PPT settings and get cooler temps, but you could handicap the max boost speeds if too low.
Curve Optimizer is also one of them things thats going to be different per CPU even if its the same CPU. You can do a negative all core value but you probably will have a core that wont like going to low, so I would recommend adjusting per core and keep and eye on the Event Viewer, if you get a WHEA error every now and then, the CPU doesn't like it.
How you can tell which core don't like it if you look at the WHEA error and see what the APIC ID is, if its ID is 0 or 1, its going to be CPU 0 that don't like that value, if the ID is 6 or 7, means core 3 doesn't like that value.
My 5900x 2 of my cores don't like much past -15, the other ones will do -30 with no issues what so ever, and thats with a +200mhz that PBO allowed to go over stock.
Good Luck!