neroden
Model S Owner and Frustrated Tesla Fan
Driving a bit more with it today, my placebo brain tells me that the MCU1 performance is actually "fine" for day-to-day use on the current firmware. (I say "current" because I'm not sure anything is radically different in 2019.24, but I specifically poked around a bit today and didn't notice any speed issues.) Sure MCU1 won't play Beach Buggy and the web browser is slow/outdated, but if it manages to run at its current speed for all the usual in-car tasks (HVAC, map, music, settings) then I personally see no reason to rush to upgrade to MCU2, if that ever becomes an option.
(I also confess that I haven't been in an MCU2 S/X or TM3 recently, so maybe my brain has just learned to deal with the slight jitters and hiccups of navigating around MCU1. To be clear, MCU1 is not modern iPhone/Android smooth, but it's not painful either, like it had gotten shortly after the v9 update.)
If you turn the maps to "map" rather than "satellite" mode it certainly helps the MCU1 speed. I don't think MCU1 can handle the satellite image download pressure under v9.