Well, for what it’s worth, my Tempest is going on 12 years old now, and my colleague’s Tetra is several years older than that… Both having been used and travelled extensively, and we’ve yet to experience any issues with the buttons.
Regardless, there should be no measurable lag, due to processor response time, when switching screens or calling up menus. You might, however, encounter some blurring if you scroll through a long list of files really quickly. This is a result of the screen refresh rate being slightly delayed by the alphabetization of files.
The only other thing I might suggest or suspect is that some operations (saving files and accessing certain menus and pages) do require two button pushes, or a combination of button pushes, that one can sometimes miss. But it sounds like you know your gear, so that’s probably not it.
Of course, if you smoke or vape around your gear, all bets are off.
Either way, all the buttons, pots, and encoders in those synths are user serviceable with minimal effort and expertise. Otherwise, DSI/Sequential will do it for you for a very reasonable flat fee.
Cheers!