It really comes down to how lucky, or unlucky, you got with the silicon lottery.
If i was to take a guess i would say getting 4ghz on stock voltage should be fairly easy, anything above that you may need to increase voltage.
To start i would disable turbo mode and find the lowest stable voltage for stock clocks and work up from there.
Example:
My 8350 at stock clocks required just under 1.1v, i think it was something around 1.089v.
I currently have it running at 4.5ghz at 1.368v, which is around stock voltage anyway iirc.