I added a few things after I originally posted my
previous comments, so please re-read to make sure you've done everything (e.g. update kexts and change screen resolution).
Also, now that you're using DP connector types, BusID 0x01 is no longer valid. You will probably need to change your connector BusIDs for DP, so read
this. Your change may be as simple as changing framebuffer-con0-busid from 0x01 to 0x05 (reverse byte order 0x05000000), but I am not sure. Display property configuration is not easy and requires trial and error. If your displays and display connectors are different from the ones described in my system specs in Post #1, you cannot simply copy my config.plist.