Weird Mouse Lag

@A_Fulcrum_Agent  The most obvious difference is that you're now running a year-old build of Windows.  I haven't heard of any issues with the current build that would explain your issue, but there are plenty of drivers and other software that would have different versions for each build, not to mention how the same drivers would interact differently with each build.  I'm not suggesting you update to 2004 just to experiment, but it's something to keep in mind for when you do eventually need to update.

You also have a slightly newer Nvidia driver, one that hadn't been released when you originally posted.  What's interesting is how new the previous driver was, and yet Nvidia replaced it just over a week later.  Maybe that's because the company is working out the finer details of supporting the new 30-series cards; maybe there was a problem with the older driver.  I have no idea; I'm just suggesting that it's possible this made a difference, since the problem could at least in theory have been related to how the mouse was rendered rather than anything else.

It's interesting you mention Nahimic.  The software occasionally blocks Sims 4 from loading at all on certain systems, usually for a few weeks before some update in the background fixes it.  I've never heard of it causing your particular issue though, or of an incomplete install being a problem.  Still, given how much of a pain the software can be, it's plausible that it was the cause.  You could also try uninstalling it entirely, or at least shutting it down via the Task Manager, to see whether it helps with the residual stutter.

When you do eventually update Windows, it's a good idea to run one update at a time, manually, and test after each one.  Windows will install a number of new drivers along with its new build, and that can't be helped, but if the problem does recur, running the other updates separately may help clarify the cause.

At any rate, I'm glad it's better, if not all the way better.