you need to stabilize your OC to enjoy the additional clock speed.
if the oc isn't stable and even you OC and the clock show higher in setting, you only facing more worst/slow/problematic scheme.

even OC in bios also wont leave evidences behind. (correct me if i'm wrong)
just reset the bios to default when sent to warranty.
that's why you still can claim warranty if you didn't admit doing overclocking.