Thank you for the tips to remove the polygons.

I play in 1080p/60Mhz on a GTX 970 + active monitor VIEWSONIC V3D245 and I keep 60fps all the time with highest graphics quality. Great !

The Carpark is more complex and there is no fix yet from the Helix mod community (http://helixmod.blogspot.be/2013/10/game-list-auto...) and the Bo3b's School for ShaderHackers tutorial is based on the Unreal Engine. I don't know if it would be helpful to fix broken 3d with the Unity Engine...

I will also look for a NVidia profile wich would help when I'll have time.