this is a bit far from what you wanted but, have you ever tried oc'ing a cpu? i am asking because i would suggest you start with that first, the cpu is safer (as far as i know), it can tolerate almost everything (except a very high voltage). If it fails, it would just reboot or give you bsod but recovering is easier in my opinion. and for most boards, if it fails to boot (i think 3 times), it will revert to default settings allowing you to boot properly and set the settings again.
if you become comfortable with that, then you can try the gpu if you want to. I just think that the gpu is already hot as it is. and can be damaged more easily than the cpu. Please someone correct me, as i am not an expert in overclocking gpu's, this is just based on what i know.