how old is it, you dont tell them what you have done you just say its unstable BSOD'ing all the time and your having to up the volts to maintain stability.
look at buying there insurance for £15 it covers all aspects of overclocking and lasts for three years.
If it's stable at stock then its not deemed faulty so he can't do that.
Unfortunately mate, most of the chips really are not that great at overclocking. If you can manage 4.75 thats pretty damn good going tbh!


much more fun.