So just did an express run on the Great Western route on the PS5. Although load times aren't noticeably reduced (I am running it off an external 4 Tb HDD), once the route is loaded the sensation of speed is something to behold. I actually felt like the train was hitting 125 mph and it was s-m-o-o-t-h, no stutters at all. Now to maybe try coming out of Augsburg using the DB BR 403.
So Haupstrecke Munchen to Augsburg does have noticeable stutters, though these are mostly confined to in and around other traffic. Just a pity it's such a busy route and some timetable runs have you passing several other trains during your run!