Well the chip gets very hot under load, but a safe place to start would be 3.8 i think, mine does that at nice temps. After you go over that the processor gets hungry for power = hotter.
Mine did 3.9 with the stock cooler, and now 4.0 with Corsair H115i (aio watercooler).
I suggest you start with 3800 mhz and 1.25 V and then you can play around from there, if it's unstable you need to up the voltage a little the max recommended by amd was 1.35 mine is set to 1.4. Beware of the temps under load! it goes from 0-60 in seconds
I suggest you have cpuid HWMonitor running to keep an eye on temps when doing load testing, and prepare to spend alot of time waiting for reboot and when it crashes, or you push it too hard it might reboot and just do nothing, the display on the motherboard can show 00, if it does use power button and switch it off and on again. It's normal after you set the settings in the bios, if you set the clocks too high and or voltages too low that the system will not boot and it reboots almost instantly, it will boot 4 times i think, just let it and when it comes back go to bios again. Good luck