As far as we know, up until now, 880M was the fastest card for M17xR3 due to UEFI BIOS issues. I got a WX4150 flashed to RX 560 and it worked with the 120hz eDP display, so I decided to gamble and bought the AMD Radeon PRO WX 7100 (mobile) MXM card.
Well....it worked! It was a Dell card and worked right away.
Everything works EXCEPT fan control! You have to use HWINFO to control fans.
The stock vBIOS barely hit 10K firestrike GPU score. I modified the vBIOS to OC RAM and increase power limit. Now it gets 13k! I can probably push it more but will try that later, wanted to share the news.
This GPU supports DX12 and the 120hz eDP panel so it is the perfect upgrade. The cost isn't too bad either on Aliexpress (eBay is a bit more).
IDT sound works too, but for me even 880M worked fine with IDT audio. I tested the GPU in Win7 and Win10 and it works in both.