Thank you

What gets me is you say your benchmark scores are where they should be but games are not playing up to par.

Some things to try:

1) Clear cmos and try at default settings.
2) Update to the latest bios.
3) Install the latest Nvidia driver 397.93 - When doing this, I do a custom/advanced install and uncheck everything except the graphics driver, physx driver and Geforce Experience as I use Shadowplay for recording gameplay. Then check the only box that says perform a clean installation.

4) Run command prompt as an administrator and type in sfc /scannow, leave a space between c and / and press Enter.
5) Run the windows troubleshooter to see if it finds anything.
6) Try a system restore to when your pc was working properly.

If all of the above doesn't help, I might consider reinstalling windows.

A memory diagnostic wouldn't be a bad idea; Rolling back the drivers for your video card for a comparison might be wise also. The Windows update for Win10 just rolled out, that might be an issue.

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3D benchmarks like Futuremark suite are designed in such a way that the CPU has little impact on performance. Non synthetic workloads such as games will show other subsystem limitations better. At this stage, I would reinstall the OS as suggested above rather than troubleshooting further.

Still having an Issue OP?

Have you been monitoring GPU/CPU temps while this is happening?

I had a friend who had a similar issue and turned out the CPU cooler block was not fully seated down on his CPU IHS fully so it caused the GPU and CPU to throttle thus causing the FPS to drop.