In case you missed this run live, Check out this Ultima VI speed run by squibbons! So glad it got run.
You can buy Ultima VI for PC(DOS) here on gog.com, and you can then play it in the free NuVIe engine. You can also modify the map with apps like the free pu6e. There are two other games Origin made with the engine: Martian Dreams and Savage Empire. I haven't played them yet.
Here's another great speed run I think about a lot, a newer version with commentary of an older speed run in which the runner beats Ultima VI in a single in-game day.
In Ultima VI, the in-game day's duration is determined by your footsteps and turns (as in, moments when you wait or do something like in DnD), so timeflow is fully-controllable by the player.
Here's the original fb UDIC post.