"Hey doc, it hurts when I do this..."
dear ksu, without looking into this any further, i strongly suspect that the newest driver simply isn't suitable for your debian version and/or hardware, hence the breakage.
it seems you managed to confirm this twice (!) and also fix it (!!) - so all's well that ends well, yes?
In this case, everything ends well! It always does end well if using Debian, or Linux/GNU in general!
I hardly doubt the installation process has anything to do with the X freezing resulting with some graphics suitable for some geek's "screensaver" after running fine for 1-2 days.
Hardware problem, maybe... only in case it is exposed by 375.39 (and -1). Comparing 660, or any other model, other than gtx9xx (GM204) series is like comparing apples to Rubik's cube.
The Debian bug system is great, unless it comes to a reopening a considered 'fixed' case - but that's some maintainers' personal problem, such as zfs-linux package on x86_64. Now, in case of a proprietary binary closed source blob, I would not open a bug report on Debian...
After reinstalling each driver at least 4-5 times, and the ca. 1mo of smooth ride before, and after '375.39' appeared, for sure I am not about to try that option again...
This post was just an FYI, for folks, that might also have a similar problem, and blame 'just' the hardware.
In any case, thank you all,