Oppinions on CPU and GPU overclocking

I was just wondering what you guys prefer.

Overclocking through the BIOs or through a program like RivaTuner?

Are there any downsides to either?

Say you overclock through a windows program and you suffer a crash where you cannot start up windows, can you still revert the settings back to normal through the bios?

I used that one tool there to oc my graphic card and it didn't do any harm to anything at all wich I'm very glad.

I have the 8600 gt xxx 256mb one and it was ok just by its self with out the oc but I decided to go ahead and oc it after all and it is running jus fine. I couldn't get the oc as high as I would like for it to be cause when I whent to go higher a green screen came up the first time and the the scond time a black screen so then I backed it off and it was ok.

Hmm if Nvidia go Ntune.I tried Ntune didn't work, froze my mouse and system whenever I started it up. So I guess I have to go with rivatuner. Nevertheless I think CPU overclockingis better done in the BIOs (I have already tried it, my mobo has a feature where you set the clock and it automatically adjusts), and GPU better done in windows (not much experience through BIOs if possible). But who am I to say, I was asking in the first place.

Thanks

Which would be done through BIOs?

/edit and also I am planning on oc'ing my 8800 gt to ssc clocks, so will my performance be affected if I clock to those speeds?

Well with me when I used rivantuner and I whent to far on oc all I got was a green or black screen but I'm not sure if that was just me or would that do to ever one.

also is it possible to oc a dual processor cause I only have a 2ghz