Hmm, weird. I just loaded up HL2 to test this on my GTX 470 and I am getting pretty crappy framerates here too. In 2D I am easily getting around 200fps average, I think 298fps is the max no matter what, and going down to like 120fps in a heavy scene. However in 3D I am just barely getting 30fps average. I think it hits around 50fps max and as low as 15fps in certain parts (even if nothing is going on). This makes no sense. I can get like 80fps in Metro 2033 in 3D, now way HL2 is anywhere near as intense. I even tried setting everything to low quality and it didn't make a difference. Something is wrong. I clearly recall playing HL2 on my old computer and I got better performance than this in 3D. WTF?!?!?
Maybe its the driver issue? I suspect the 3D driver, since its works fine in 2D.
And in my case its even worse 10FPS.
You should install MSI Afterburner and enable all the Monitoring features and in setting choose to show them on the screen.
When you run the game you will see how it works and if your power state lowers when you enable 3D.
P.S. How you can get 80FPS in metro and in 3D? did you lower all the settings?
Last time i checked this game on GTX580 1920x1200 AAA enabled, Physx Disabled DX11 = 33FPS in 2D
And this is serious benchmark PChttp://www.guru3d.com/article/geforce-gtx-570-review/16