Hello, I'm pretty new to overclocking and already understand most aspects of it by reading the posts and google, but what have been confusing me are the FSB and MCH voltages.

Can someone please explain to me how will I know if I need to increase them?

For example, say I overclock an e6400 to 3.2 ghz (400 mhz) with 1.35 vcore, I run some tests (orthos, small ffts) and it fails.

I've run memtest on my memory with the timings I want overnight at 800 mhz and there were no errors.

Now what I know so far is that here is where I up my vcore and try again, until I get it stable without failing orthos.

So my question is :

1) When exactly do I need to up my FSB or MCH voltages? How will I know? Or is it just guess work?
It is a guess work... increasing MCH voltage is needed if overclocking on INTEL chipset board.... normally oc more than 3ghz MCH must be increase to gain stable pc else u will love to see BSOD.

2) Will upping my FSB or MCH allow me to run at a lower vcore ? Or it does not work that way?
No way.. CPU and Chipset Core is not working that way... want a fast car running more speed and want to save petrol? =x
unless the car itself can running faster with low vcore then it is fine.. consider lucky you

3) If yes, FSB/MCH voltage vs. Vcore, which one is the better one to decrease/increase in terms of being safer, more stable, long term usage, etc. (i.e +0.1V on FSB is better than having to increase +0.05V on Vcore, something like that, if it works that way anyway)
Wanna overclock make sure cpu heatsink is not original and better cooling...
good pure power supply is needed and if it is intel it is MORE needed a better power supply if wanna clock...
no body can know how my cpu need how much vcore to gain how much overclock i can...
at first clock cpu until u think it is fine with good prime 24 hours... stable...
when gaming or something else pc hang .... that might cause mch have not enough power.... so increasing it will helps to gain stable system... easy word ( if original 1.20 u need up 1.40 something)
so u need more reading on that topic...read more is the key ..
some ppl like to try give cpu more fsb 1st and increase vcore with it slowly...
some like direct give a power vcore shot and gain top cpu speed .... then drop down vcore slowly and prime it... stability test... ( that is me too ) so need make sure u have good cooling ...

That's what i know

Will really appreciate it if someone can answer these questions 

Thanks in advance