There is a known overclocking bug on X58: when you hit high BCLK and/or high QPI link (3800+), sometimes the PC won't POST, happens randomly. Raising PCIE by 1-3 MHz solves this problem.
Google around, you'll see a lot of people suggest it on X58. And yes, raising PCIE frequency is dangerous WHEN its more then with just a few MHz.
EIST = Intel SpeedStep, power saving technology (downclock CPU when not in use), it only works with dynamic voltage. When you set static (fixed) vcore, it does downclock but without voltage reduction, so its useless. If you're interested in power saving, only C-states (CxE Function in your BIOS) work with fixed vcore, but BCLK must be 162 or below, otherwise you may encounter BSODs when idle. If you wish to keep SpeedStep, your motherboard must support dynamic vcore, and you have to add an offset.