Well lower res is easier for a GPU to handle. At 150% scaling you're taking a ~33% performance hit (over running at native res), and higher scaling does introduce input lag.
For comparison:
1080p @ 150% scaling = 2880x1620 = 4,665,600 pixels
900p @ 150% scaling = 2400x1350 = 3,240,000 pixels
In other words, 1080p at 150% scaling is 31% less FPS than 900p would be at 150% scaling. Because the GPU has to work a lot harder to render each frame.
The 1060 isn't particularly powerful, so if you want to run at that scaling at comparable FPS you'd need to turn some settings down.
I'm guessing you mean PLS for the display, if your old monitor was a years old or cheap IPS/TN it probably didn't look near as good as the new one.