OK, I figured it out.. but still no solution.
The issue only happens when I have a second display connected to my laptop. So, if I hook-up a big monitor and use it as the primary display the code editor slows-down. Using the code editor on my laptop's monitor (without a second display connected) everything is good-to-go.
Now, my laptop (it's a new Macbook running Windows 10 x64) is always connected to a second monitor when I'm in the office so this is a really bad situation to have.
Anyone have any ideas how to fix this..? much appreciated.