Updates:
Ok, so after reading some of this guide about overclocking i7 920's
Intel Core i7-920 Overclocking Guide - X-bit labs
and then I read this entire thread here about overclocking i7 and how it affects memory frequencies, uncore frequencies and QPI frequencies.
ASUSTeK Computer Inc.-Forum- Overclocking Intel Core i7 processors
After reading said guides, I came to the conclusion that the stability issue could be caused because my QPI multiplier was not greater then the Uncore Multiplier at a 9:8 ratio, based on the default clock speed (blck) i was running which is 133mhz. Which in that 2nd guide, it mentions that it should be, for best system stability during overclocking (I highly recommend anyone who's just learning how to overclock to read that btw - it really helped me understand a lot in a relatively short amount of time).
On the default configuration the store had set my computer at, all they did was set the dram frequency to 1600mhz (on P6T mobo's they don't show this in multipliers, they just show the frequencies themselves), so effectively they changed the memory multiplier to 12. The Dram Bus Voltage was set to 1.66, and timings set to 7-7-7-24. Everything else was set to auto.
First I dled CPU-Z to check what the mobo had decided to set the uncore multiplier at (or the uclk frequency if you times ur base clock with the multiplier), and then the QPI Multiplier (aka QPI frequency divided by bclk divided by 2). CPU-Z had them at the same values.
Again, confronting that guide I mentioned earlier, your QPI Multiplier has to be > then your Uncore Multiplier by a ratio of 9:8 to achieve best system stability.
So essentially, by leaving those settings at auto, made it run both those multipliers at 24 because my memory multiplier was manually set to 12. Thus leading to system instability when running Prime 95, or when running programs that stressed the computer a lot.
In fact, if you refer to the chart shown in that overclocking guide you will see that when using default blck of 133, only a maximum of 1333 dram frequency can be used without having your QPI multiplier = Uncore multiplier or having your QPI Multiplier < Uncore Multiplier (which again, could result in system instabilities).
So what I decided to do was just to underclock the ram settings.
I lowered the Dram Frequency to 1333mhz (effectively changing the memory multiplier to 10). Then adjusted the Uncore frequency accordingly to 2666mhz (uncore multiplier of 20). Then adjusted the QPI multiplier so that it was greater then the uncore multiplier to a ratio that I could achieve that was closest to 9:8. This was achieved by setting the QPI Freq to 5866 (or a QPI multipier of 22).
I then adjusted the Dram Bus voltage down to 1.64 from the 1.66 it was currently at. Kept the timings at 7-7-7-24. Then left everything else at Auto.
So far, ive been running Prime95 Blend test for a bit over an hour with no errors or computer restarts. Temps over all four cores are about 64-65 on full load. Will leave this on for the night and post a followup on the results.
I could probably also lower the dram bus voltage a bit more, and tighten the timings for the ram whilst still keeping things stable. Anyone have any recommendations for this?
Lastly, if you confront the chart shown in the 2nd guide I posted, you will see that it is not possible to run dram frequencies of 1600mhz or greater on a default blck of 133mhz, since by doing so, you won't be able to get a stable ratio for the QPI:Uncore multipliers. Therefore if you wanted to do that you would have to overclock the blck and adjust the memory/uncore/QPI accordingly to achieve that 9:8 ratio. So basically in order to do so you would have to overclock the blck to at least 160mhz and then adjust the rest of the multiplier values accordingly (as shown in the chart).