Also, is it possible to use clamshell mode without closing the lid? So, I can use external monitor only, and don't be afraid of potential damage to built-in display, and also use built-in speakers.
[Edited by Moderator]
I've had the same issue with my MBP 16". I had heat issue and performance degradation with 2 4K external monitors. After change internal configuration without success, I've bought a dock station with external power supply. There's no issue anymore. The solution is an external supply for the dock. The dock that uses the MBP battery or power supply doesn't fix the issue. Now I'm using HDMI and DP at the same time, the lid is closed and the temperature is 58C and the fan is running at 1896 RPM.
Turn the brightness all the way down. Technically your mac will still be using two displays but it will work so long as you set mirroring and choose the resolution more adequate for the external.
MBP 16" external monitor heat issue (not clamshell mode)
