Hi Ivan,
great to have you on board here! I have scheduled the benchmark (along with putting in a new harddrive) for the Xmas break, promise!!!
Benjy, I guess that you have probably already started with Ivan’s suggestions. My vote for the first step is on the excellent idea to just take a different drive (sounds like you have plenty) and create a new windows install without nuking the old one. That way you can easily roll back without any issues. Think about removing the old drive entirely for that. I agree with Ivan that messing with the Registry can do more harm than good, expecially if you are not familiar with it. Plus you can never be entirely certain what kind of keys RC adds to it anyway…
I can’t imagine that it’s down to the Promo as opposed to the CLI since, as Ivan says, they are (or should) be identical except for the restrictions. Of course, there is always the unpredictability of complex software. But, as you said, the success of the Steam Demo proves that it’s not the imagery nor the algorythms per se but some permanent corruption. Did the guys from RC provide you with their project file yet? Should be another clue how that will behave in your system (first only texturing, then reconstructing plus texturing and finally realigning with the following steps) - if all succeeds, then the error is somewhere in the first files that RC spews out, if not, then it must be in the Registry somewhere. At least in the imagination of a non-programmer (that was the third neuron today, btw… 
In any case the DEVs should be very interested in all this because it points to a serious bug. You might be responsible for homing in on the cause for those random crashes tormenting people in the past!
I am sure the end is nigh…