Gtx 650 ti overclocking problem.

Hi everyone,I have some kind of an issue because i've recently bought a gainward gtx 650 ti,and i did some overclocking,but as the gainward utility did not showed that the core clock was modifying i tryed to set it up to +378 or something like that.Instantly the screen turned black and i coldn't do anything else.So i quickly restarted my pc,and everything was back to normal.On the other hand i read that increasing the voltage also increases the performances,so i set that to +25mv and after that i've read that this thing can cause damage,so i've lowred it down to the stock values.The big question i want to ask you:Have i done any permanent damage to my graphics card?I really hope not,thank you in advance,and sory for my bad english.