I bought my Y50-70 without a pre-installed OS and I struggled with the drivers but have not been able to get my notebook make use of the built-in Nvidia GeForce 860M.
I reinstalled Win 8.1 (again), followed by updating
- both chipset drivers
- storage drivers
- energy managment drivers
- Intel video card drivers
- Nvidia video card drivers
from the Lenovo download page - nothing else except one game for testing. And that worked, the game ran perfectly - until I rebooted.
Now it's the same situation as before. Both (Intel and Nvidia) drivers are proper according to the device manager. But the game (Planetside 2) runs with 20fps again - instead of 90fps before rebooting. I have the laptop connected to a larger external monitor.
Ensure that your laptop lid remains open when in use as the integrated Intel GPU will not kick in.
When the lid is closed the integrated Intel GPU is used while the lid is closed.