So i have now superstable settings like this:
CPU voltage 1,375v
RAM: 1.68v (1,65 real)
CPU spread spectrum: 0.30%
This means that frequencies generated on CPU MUST be same as on stock frequency and do not contain any noise, or are not different. My secondary indicator - VBAT shows 3.3v at all times, and the test at 40 degrees has Passed.
CPU voltage with Spread spectrum ON: 1.375v
CPU voltage with Spread spectrum OFF: 1,275v
This difference shows how much can the spread spectrum consume, but also shows how much is CPU tolerant to different character of its own frequency. Lower CPU voltage also means lower frequency amplitudes and temperature of course.
Now to bit OCing of X48. I decided to go forward very slowly. +1% each step of FSB. That means +4Mhz on FSB and +1Mhz on PCI-E. Here are steps i actually tested. I decided to set frequency of memory to 400/1066. I am testing just the CPU and X48.
100% - 400Mhz FSB - 100Mhz PCI-E - Base and well tested frequency
101% - 404Mhz FSB - 101Mhz PCI-E - Works fine without any other settings
102% - 408Mhz FSB - 102Mhz PCI-E - NB voltage increased. VTT inreased
103% - 412Mhz FSB - 103Mhz PCI-E - Dead Frequency. System cannot POST
104% - 416Mhz FSB - 104Mhz PCI-E - Voltage to SB added.
105% - 420Mhz FSB - 105Mhz PCI-E - Dead frequency. Graphics cannot start on OS with this PCI-E
106% - 424Mhz FSB - 106Mhz PCI-E - Bit more voltages, but still works Fine with CPU spread spectrum.
CPU skew rates are still default.