PCIE Frequency and volatge - What, Why, how?

I have a current problem listed on another thread, which has lead me to want to understand the the topic if this thread: PCIE Frequency and volatge - What, Why, how?

I have always been told PCIE frequency should be 100mHz, or auto. I've heard little about increasing PCIE voltage, potential range is +0.1v to +0.3v, mostly to the effect that it has no effect.

I do however believe that the motherboard manufacturer would not put these settings in the bios, unless they served a puprose.

So my questions are: If you should never change your PCIE frequency or PCIE vol, as I have been led to be believe: Why are they there? What can I do with them, related to performance and system stability? How do I use them to my advantage?

I've head some stories about a specific few video cards that get a boost in performance by increasing the PCIE frequency. I've also heard of people increasing the PCIE frequency for improvements. I've heard very little on PCIE volatage, mostly saying that is too small an increase to do anything.

Please post whatever knowledge you have or of heard of, and help me and the readers of this thread come to an understanding of what these settings mean, and how we can use them for improved performance and stability issues.

With X58 and P55, increasing PCIe frequency may help you reach a higher bclk/FSB. I try to keep it at 100MHz, but I've had it up to 115MHz when testing for max bclk/FSB. I've tried increasing PCIe voltage and it would get me a couple more MHz PCIe frequency, but that additional PCIe frequency didn't net me any more bclk/FSB, so it was kinda pointless.

I've tried increasing PCIe frequency on X48 and P45, but it doesn't seem to help at all on LGA775...

I have no clue about AMD, I've never even seen an AMD CPU or motherboard in person, much less used one...