I think the overscan works well. Even on sections where you're walking around something that is one block from the edge* I wasn't accidentally moving to the next section accidentally. And it feels more deliberate when you do transition, too.
*like here. Going from bottom, to right, to top without stopping required you to be a lot more precise before but is a lot more manageable now:
I think the diagonal works well, from a speed point of view. I think I could tell it judders at first because I was looking for it, but after a few mins forgot about it so it's probably not as noticeable as I first thought. But when I keep thinking about it then it is still noticeable. Actually, I think it was less noticeable depending on where I was - certain parts of the map you can only really do diagonally one or two squares so you don't really have time to notice it, but it's a lot more prominent in open areas, which are less common, since you have more time with the effect. And then I was specifically using these open areas to test it, which is really looking for an issue that might not be too obvious in most circumstances.
And with the introduction of more NCPs it's feeling more and more game like.