Are there any downsides to reducing the voltage on a CPU? I know it reduces temps and could extend the life of the CPU, but how far could you go (for example with my CPU)? For example: my stock voltage is 1.375v if I reduced the voltage to 1.3v or even down to 1.25v would there be major instabilities?
No disadvantage so long as it still tests as stable, so undervolt, test, undervolt, test... until it starts crashing or producing errors, then up it a fraction. Same methodology as over clocking really. I undervolt AND underclock my server, as it doesn't require CPU grunt at all. It has a decent , proper hardware RAID card to handle parity calculations, so the CPU is essentially doing very little. It's a Celeron E3200 and it's now running at 0.89v at 1GHz.. it runs that cool I could probably just cool it passively.... and uses about 90 watts when being used, and around 40W idle. Probably half that power is the HDDs themselves.
That's pretty much the whole point of undervolting. As low as the cpu will go without being unstable and crashing out. Some recommend going down in little steps, others suggest fairly large steps to map out a possible range then the little steps. However, one thing that i never really managed to figure out. How do you test the stability of the idle states? Just let it be and see if it crashes out?
Pretty much yes. Leave it on overnight for a few nights. If you plan on using S3 make sure you test that too.
Well I've tried 1.25v for my CPU and I haven't had any issues yet that I could see, was playing Skyrim for a few hours with no problems with a reduction in temps by roughly 10c.