Im just gonna put these here... We'll see how long these last.
These are a few videos I recorded using Shadowplay in fullscreen mode, on my GTX 670.

1. http://youtu.be/073v1ddJ71o
2. http://youtu.be/w86RYMwYSM4
3. http://youtu.be/6zwm0avy_T0
4. http://youtu.be/JeHSnGkysVU

In short, when more people seem to be logged in the game, the lag magically turns on.
During off hours, the lag turns off... and then it just magically turns on again.

Hell, just this morning I did a Expert DF and everything was fine. Perfectly beautifully fine.
This evening, I can barely run around town, and as soon as I step foot in a dungeon, and combat starts... yeah, 0 fps slideshow.

I have gotten to the point where I am just going to reimage my computer, and see if that fixes whatever BS is causing this... If not, well I guess I could update to a newer video card... And if that doesnt fix it... meaning there is no issue on my end... Well SE, the ball will be in your court.