Your low temps are more than my high temps, and my system is OC'ed to 3.84 GHz on air cooling.
Your system is running too hot, the CPU will throttle down to prevent damage.
What ever is causing your crashes is being made worse by the high heat.
Did you buy this system complete and already overclocked?
If you bought it already OC'ed, should get them to sort it out.
It takes a lot of patients and testing to get a system OC'ed and stable.
I don't know anything about the company you got this from but, if they are plugging parts in and slapping an OC template in BIOS and pushing them out the door, it's going to be trouble.
All components perform differently to some degree. This is why each system has to be slowly tested to find it's limits, they will all be different. Even if they have the exact same parts.
What do you have for CPU cooling?
Intel's recommended CPU temp limits are 68°C.
Intel® Core™ i7-950 Processor
Tcase 67.9°C
Tcase is the CPU case, add 5°C for the CPU cores, 73°C.
The CPU will start throttling down around 68°C core temp, you are passing that.
Your CPU stock clock speed is 3.08 GHz, if your using EIST it should idle at that speed.
What method did you use to set the CPU clock speed to 2.67 GHz?
Can you download CPUZ and post a snip of the CPU, Mainboard, Memory, and SPD tabs.
Do this when your system is at idle.
Post the core temps when the system has been at idle and temps stabilized.
Then snip the CPUZ CPU tab when it's at full load.
The next problem I see after the heat, is the RAM timings are too tight, when you OC to a high frequency you will usually have to loosen the RAM timings to get stability.