I just found a solution to a problem that I've been pounding my head against since I've started playing.  It's from a post from Nov 26, 2012, but the bug still exists.  Do the devs know about this?  It seems like a bug that drops fps to 2-4 after a random time playing even if you look down or at a hillside and lasts for a minute or two would be a priority.  Especially when the solution has been pointed out on the forums...
 
 
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2. Then Use the Settings in this Screenshot below to fix the current threading issue.
And Make Sure you Apply it before closing the Control Panel and Running MWO.
 
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from: 
http://mwomercs.com/...vidiaamd-users/