Hi everyone, hopefully I'm not too late to contribute to this discussion.
It's been quite a while since I installed the P4200 in my Alienware 18.
Recently, out of curiosity, I decided to try something different by modifying the INF file and installing the GeForce driver instead of the Quadro driver.
After doing that, I noticed my laptop started behaving strangely. The GPU was no longer performing as well as it used to, so I began investigating the issue.
Eventually, I came across this thread and realized I was experiencing the exact same problem. My GPU was being power-throttled at 50W.
However, I'm certain my P4200 never had this 50W power limit before.
Here's what I did to restore normal performance:
Used DDU in Safe Mode to completely uninstall both the Intel and NVIDIA drivers.
Rebooted and disabled Driver Signature Enforcement.
Installed the GPU driver first (I used an INF-modded version: 582.53 Quadro RTX Desktop/Notebook DCH WHQL).
Without rebooting, installed the Intel graphics driver (win64_15.40.5171.exe).
Rebooted the system.
After following these steps, my laptop returned to normal and the GPU was no longer stuck at the 50W power limit.
One small trick I still have to use is manually setting the fans to 100% using HWiNFO. Otherwise, the GPU will still power-throttle, even when the temperature is only around 60°C. I suspect this may be due to the VRMs overheating rather than the GPU core itself.
I hope this information isn't too late and helps anyone else who runs into the same issue.
Attachment is to show the GPU Power Limit and your motherboard/ec power limit.