Hi. I found solution for unworking nVidia (my geforce 820m + intel hd 4400 graphics, laptop) card on the os win8.1x64 !
I'm read all forums, that forum, my brain so BLOW BOOM! And... >>>
Game too old and not to see D3D dlls (direct X 8, 9). dgVoodoo and old dlls for old d3d helped me to start SimCity on nvidia! FPS grew to 40-60, and for "hardware" mode but on the Intel FPS = 10-22 in a city. In a region FPS is about 200-400.
Oh... A whole year of infrequent but long searches... So tired:)
For info:
SimCity licensed and stay on steam
laptop acer
os win8.1x64 (by the way - on a win7x86 game started without crutches on the nvidia card!) - as practice and observation have shown - it's a matter of directX dlls (d3d dlls), that "slips" by dgVoodoo to game *exe. For use need to read "readme" for that soft.
I hope I helped someone.