Terrible performance for me too
I also have terrible performance, even on low settings. I have a laptop with Optimus, but the game IS using the nVidia card, not the intel crap.
From nVidia Control Panel System Info (dxdiag won't read the GeForce)
[Display]
Operating System: Windows 8.1, 64-bit
DirectX version: 11.0
GPU processor: GeForce GTX 680M
Driver version: 334.89
Direct3D API version: 11.1
Direct3D feature level: 11_0
CUDA Cores: 1344
Core clock: 719 MHz
Memory data rate: 3600 MHz
Memory interface: 256-bit
Memory bandwidth: 115.20 GB/s
Total available graphics memory: 12232 MB
Dedicated video memory: 4096 MB GDDR5
System video memory: 0 MB
Shared system memory: 8136 MB
Video BIOS version: 80.04.67.00.01