Yeah I gotcha.
Try this site. http://hwbot.org/
Others that have similar equipment pool into benchmarks. It often mentions what their settings are so you have an idea of how far you can OC. (max speed applied etc...) Might also help you get an idea on where to start off.
The best advise I or anyone can give you. Is read a few OC guides and start off slow.
I personally would do the following.
Push the system to max (in small increments) using stock voltage and settings. Simply slowly push up the OC on it until the OC becomes unstable. Then back it down until you find a stable point. Should be able to run benchmarks and reboot without problems to indicate a stable OC on stock volts and frequencies.
I'd then start playing with volts and frequencies (in very minimal increments) to see how far I can push my system. Every incremental push on the OC. I would stop and run benchmarks and tests to ensure it is stable before pushing it again.
Things to be careful about is pushing your volts to far for your equipment. Make sure to look at the link I provided plus google for others to find out what the max volts recommended is for your equipment and do not surpass that!
Also be careful as added OC and volt also increase heat. So make sure to be monitoring heat while you are apply OC.
This is pretty safe since newer machine often have sensors to force shut down a PC if the OC or heat becomes to much. However, it is always better for the hardware if you catch it before it even reaches that point. You can use tools like HWMonitor or MSI Afterburner etc... to monitor temps.
There are multiple ways to OC. XMP, manual OC and even some boards have prefined OC templates (outside of XMP).
This is why reading about OC Guides and your equipment directly is important when OCing.
I wish I could offer you a better starting point but honestly, unless I was sitting infront of your PC doing the OCing myself. I can't give you any numbers to use directly. That comes from experience and based on your exact hardware.