what is the highest i could run vNB for 24/7 use?

I threw my Xeon chip back in and am trying to raise the clock from 3.5ghz to see how high it will go for 24/7 use, i've boot at 3.9ghz so i know the chip can go higher. i'm currently working on 3.64ghz (8*455) but so far have vNB at 1.43 and failing Orthos. Load temps are all under 47C. Maybe i need to tune gtl's on it first?