Not particularly risky unless you mess with high voltages.
As to benefit, do some testing:
a) Run your games, but lower your resolution and eye candy.
If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics configuration, and no OC is necessary.
If your FPS stays the same, you are likely more cpu limited, and overclocking will help.
b) Limit your cpu, either by reducing the OC, or, in windows power management, limit the maximum cpu% to something like 70%.
Go to control panel/power options/change plan settings/change advanced power settings/processor power management/maximum processor state/
This will simulate what a lack of cpu power will do.
Conversely what a 30% improvement in core speed via overclocking might do.
To prove/disprove the value of 8 cores, you could also experiment with removing one or more cores. You can do this in the windows msconfig boot advanced options option. set the number of processors to less than you have.
This will tell you how sensitive your games are to the benefits of many cores.