E8500 Won't Pass IBT > 4.0ghz (Need Help)

[LedHed]

So I have had my E8500@4.5ghz 1.45V, but I never tested it on IBT until last night. I clocked it up to 4.2ghz (525x8) 1.35V and it would only pass 80% of IBT no matter what voltages I tried. However I can run 4.0ghz @ 1.23V and IBT doesn't even get the chip up to 70C after 40 passes, so I don't understand why with all that voltage increase I can't pass IBT 100%...

My Voltage settings @4.2ghz were:

CPU: 1.35V
DDR: 2.3V
Chipset: +0.250V (1.36V)
FSB: +0.250V (1.33V)
CPU 1 GTL: 0.63VTT
CPU 2 GTL: 0.63VTT
MCH GTL: 0.59VTT
CPU PLL: 1.6V

FSB/NB Latch: 1333mhz
PCI-E Freq: 100
GPU Clock Skew: 200ps
MCH Clock Skew: 300ps
CPU Clock Driving Control: 900mV


My RAM is running at 1050mhz (1066 Rated) and my PL is at 12T

I chose my hardware for this system based around max OCing and I know this board can easily push the E8500 to 4.5ghz and beyond, but IBT doesn't like it over 4.0ghz.

Does anyone have any idea what I can try to get a stable IBT run @4.2ghz based on the settings above? Or any ideas in general will be appreciated.