Your going to need more voltage for 4GHZ, Most Thubans hit a wall around 4-4.2GHZ. Just keep increasing voltage till it's stable. The reason I recommended increasing the bus speed is because i can hit a higher frequency with lower voltage by doing so. Since 1.45 was unstable try 1.475 but keep an eye on the temp. I'm not too familiar with your cooler.
For example on my 1100T
3.8GHZ stable at stock voltage
4.125GHZ stable at 1.4875
4.25GHZ stable at 1.535 -> I cant cool this when ambient room temps are high though so I don't use it (summer).
You can see how it starts increasing pretty drastically with very little increase in the clock past 4GHZ. The max safe voltage is 1.55 so as long as you stay under that and you can cool it your processor will be fine. Also, the max temp of the 1100T is 62c so if you increase your voltage and start getting a blue screen check to make sure you are not overheating with core temp.
As for why you were stable and now your not, that happens just means you were not 100% stable. I ran 4.125Ghz at 1.475v for 8 months with no problem. However, if I do a prolonged stress test or folding I will bluescreen after a few hours. At 1.4875v the bluescreen never occurs.
Papadope I tried increasing bus speed to 250 and x15.5 and it would even post.
It's possible your particular processor does not like an increase in the bus speed. However, are you sure you reduced the multipler's on the Northbridge, HyperTransport, and RAM to put them back within spec?Edited by Papadope - 11/30/13 at 9:48am