No problems mate:

My settings for 4.2Ghz on the key volts you mentioned are below:

1) vCore - 1.382 (real via CPUZ)
2) CPU PLL - 1.61 (real via Everest)
3) CPU VTT - 1.38 with 70mV GTL references for cores 2 & 4 in BIOS

Hope that helps.

All in all you are on par with your current volt settings. The above volts were set quite a while ago (around Nov 08) so I was a little new to the Q9650 back then.

I think you can lower CPU PLL and VTT a little more as I passed 1 hr prime blend using 1.34vtt with 4.4ghz...overall the above are relatively safe and I don't have a problem using them 24/7