ok, over 130 hours played. many many many tweaks done now, what I feel, is my best vid set up.
all was running extremely well until recently when I started getting random lockups. Primarily during night travel for some reason.. but the occasional day travel lock up as well. So back to tweaking.
The three noticable tweaks that have made a difference
pre rendered frames.
forced off vsync.
and the one that has oddly enough stopped my random lock ups. Antialiasing trasnsperency. I set this to "off". where as before it was set to multi sampling. Multisampling is the best way to go if using AA.. and multi helps with between areas like fence posts and the like. Should have nothing what so ever to do with random lock ups. But once I set this to off. I no longer have had any lock ups for the last 20 hours or so. Odd.
at any rate.. it may or may not work for you. just thought I would share what has worked for me.

of course now that I have said this.. I most likely will start getting random lock ups again.. lol.
cheers
d
ps. this is specific to lock ups.. not ctd's, bsod, loading lockups.. ect. I have had no issues with those types of problems.