Hi weird one
It is very satisfying polishing up old walls to look and feel better than they ever were. If that is weird, count yourself in amongst a big group. Do you have a CEROS DEROS or FESTOOL sander?
2 excellent paint choices, no way of saying which is best! Down to colours I would think, getting exactly what you want.
A brilliant tip I had from the master of polishing and painting walls, Andy Farrell. The Mythic is a thin, smaller paint molecule , so you would use say a 320 fine abrasive on the TX120 and the paint would fill the small holes so to speak, and lay flat. A heavier body paint, I would think IM, on the final pass with the sander, use a slightly coarser grade, say 240 to create bigger holes for the thicker paint to hide. My explanation is not very scientific, more graphic, and it is not an exact science because of each person’s technique and abrasive, but now you know the principle, try a section to see what grade helps your paint lay flattest.
E-B would be real belt and braces, and very encouraging to hear that as a suggestion.