Basically, everything looked blurry or fuzzy. For whatever reason, the taskbar, Metro UI, and other native Windows stuff was fine - but every other application just looked bad. I soon realized that applications were actually "zoomed in" - for example, I made an image in MSPaint which was 1680px wide, as a scale, and the image extended a quarter of the way on to the monitor to the right of it.
I did a little digging, and I figured out it was actually Windows resizing the stuff to accommodate for what it perceives as a much larger resolution. It must count the pixels, not realizing it's actually a 3x1 ultrawide display, and assume it's something akin to a Retina display, or a 2560x1600 on a tablet or something, where scaling like this would make sense.
I did some more digging, and it turns out this feature was indeed added in Windows 8.1: http://www.techradar.com/us/news/software/operating-systems/windows-8-1-dpi-scaling-why-you-shouldn-t-bother-getting-excited-1161343
So here's how to fix it:
- Enable Surround
- Control Panel -> Display -> Screen Resolution -> Make text and other items larger or smaller
- Click "Let me choose one scaling level for all my displays".
- Under "Change the size of all items", select "Smaller - 100% (default)".
- You will need to log off and back on to finish the process.
And that's just about it. This new feature seems to be a refinement of the old "adjust font sizes" setting, which scaled only font sizes. Windows 8.1 scales *everything*, much like web browsers evolved from scaling just text to scaling the page itself. Unfortunately the detection of the "need-ness" of this feature is broken by Surround.
I'm also happy to report that Surround works just the same way as it did on Windows 8. WIN+P works for switching between "gaming" and "working" modes.
Hope this helps somebody out!

