I've marked this problem as solved as it's almost been a week since the last BSOD crash (both on boot and while using photoshop).

Based on what I have read and how my computer was behaving, and advice given by axe0, I am quite sure that the problem was the Nvidia graphics driver.

The driver version I had installed was 361.43, however I suspected this to be causing the crashes, so I downgraded the driver to version 359.06. I also uninstalled ALL NVidia-related software when i took out the newer driver, includng Nvidia PhysX software and NVidia GeForce experience (both which I never used).

(for those interested, the site to get older drivers is here: http://www.nvidia.com/Download/Find.aspx?lang=en-us)

I will continue to monitor this problem, but I believe it is solved for now...

Thanks to all who helped!