The original S/X panel is a 17" 1920x1200 - those 16:10 panels are very hard to come by, so Tesla probably has them custom-made instead of being some commodity panel from a panel maker.
If it's a "Retina" display then by Apple's definition (2x) that would be 3840x2400 (that's higher than 4K due to the 16:10 aspect ratio).That seems excessive for an in-car display.
If it does have a higher resolution, my bet's on it being 1.33x or 1.5x (2560x1600 or 2880x1800) - though those pixel-dimensions are atypical.
I've updated the "Do I have the Intel MCU?" page to include information on screen resolution - can someone with the old and new MCUs take a photo and let me know what it says?
https://jsfiddle.net/qja8wjxc/30/show