Use Windows 10's individual display scaling to perfect your multi-monitor setup
Windows 10, like Windows 8.1, includes an option to adjust the DPI (dots per inch) scaling on a per-monitor basis using a percentage scale. This wonderful tool gives you more granular control when you're using monitors of varying resolutions, rather than applying a single DPI scaling percentage to all of your monitors--which can result in nasty sizing wonkiness--as older versions of Windows did.
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Per monitor action
To get started, right-click on an empty space on your desktop and select Display settings towards the bottom of the context menu. Alternatively, you can go to Start > Settings > System > Display.
Once you're there, you've won half the battle. You should see a graphical layout of your monitor set-up. In this case I have a laptop display labeled 1 and an external monitor labeled 2.
Underneath that you'll see a slider called Change the size of text, apps, and other items: 100% (Recommended). This is where we want to be, but before you start moving the slider around, check to see which monitor is highlighted.
In this case, the laptop monitor is highlighted in blue, but I don't want to change the scaling for this display as the 1366-by-768 view is just fine. The larger 1080p monitor, however, would look better with a little scaling applied.
All I do is click on monitor 2 in the Settings screen as seen above, and then start moving the slider. Windows 10 offers pre-sets for each monitor. In the case of this 1080p monitor my choices were 125, 150, and 175 percent, while the laptop's 1366-by-768 display maxes out at 125 percent. Your mileage may vary.
Once you're happy with the scaling percentage you'd like to try, hit Apply and that single monitor's scaling will change while the others remain the same.
You'll also see a warning that says you should sign-in and out again from Windows to make sure your apps look their best. That's no joke. Definitely sign-in and out again at this point. This may be a crucial move for some. In my initial tests, the taskbar disappeared after I scaled up and I only got it back after signing out.
Once you're back, you may notice that some apps completely suck at the new resolution, while others rock. If I had to guess this is more about developers packaging low DPI assets in their programs than anything else.
Using per-monitor scaling isn't a perfect switch right now, but at least the taskbar is easier to see and Windows itself looks great. For more resolution scaling tips and tricks, check out PCWorld's guide to making the Windows desktop look good on high-res displays.