I know I've seen many forums covering this topic (including this one) but I just recently installed the 980m in my M17x R4 with the 120Hz screen. I found an interesting trick that helped tremendously. Just wanted to share in case it may benefit someone else. I won't include all of the steps to the process as those are thoroughly covered elsewhere.
Okay, so you have the card (980m) installed but it doesn't recognize it yet (no drivers / need to change bios settings etc.) meaning that you immediately get the 8 beep error on startup. A lot of forums say you need to reinsert your old graphics card to access menus, then switch it back to 980m. I've found that through using the HDMI out and connecting to another screen, it will actually stop the 8 beeps and you regain post. It will post only on your laptop, not the screen connected through HDMI. I believe this is due to the 120Hz not being supported when connected to an external screen, it makes it function as a 60Hz and seems to resolve the 8 beep posting issue making it possible to change your settings and even install the (modified) drivers on the desktop.
I hope this helps to ease someone else's process in the future.