I've had to reboot twice today. I'm plugged in via MiniDP to a 4K Dell monitor that worked flawlessly with my MacBook Pro before High Sierra.
late-2013 MBP, i7, 16GB of RAM, NVIDIA 750GT GPU + Intel Iris Pro, no custom things about this machine at all. Here's the video. No slow-down this is real time, the screen was refreshing at roughly .5 frames per second to my eyes and this was me trying to close applications.
I have iStat Menus set to refresh as fast as possible as well and you can see in the video how slow it was
Also, every time I boot up I get this error:
Went to NVIDIA and downloaded the latest driver. Still seeing update required.
late-2013 MBP, i7, 16GB of RAM, NVIDIA 750GT GPU + Intel Iris Pro, no custom things about this machine at all. Here's the video. No slow-down this is real time, the screen was refreshing at roughly .5 frames per second to my eyes and this was me trying to close applications.
I have iStat Menus set to refresh as fast as possible as well and you can see in the video how slow it was
Also, every time I boot up I get this error:

Went to NVIDIA and downloaded the latest driver. Still seeing update required.