I've connected up the Serial Display block and written some test code to just run it up in simulation.
it looks like it can get a screen update in approx 163 ms. As mentioned previously the Doherty Threshold is at 400 ms so if there is any lag in the response it's not down to the display mechanism.
The next step is to get the design resynthersized and tested using a terminal on the laptop.

Once this is looking good I'll start looking at the input side of things and see if it works as well.

Note that I improved the UART block again as the original interrupt logic was just pants for the TX side. I have a suspicion that the RX side will not be any different !