Sluggish performance using fullscreen 32 inch 4K monitor

• iTerm2 version: Build 3.2.7beta4
• OS version: 10.14.2 (18C54)
• com.googlecode.iterm2.plist
• debuglog.txt
• iTerm2Sample.txt

Hardware specs:

Detailed steps to reproduce the problem:

1. Open iTerm in non native full screen.
2. Open split.
3. Wait for far too long.

What happened: Sluggish performance opening splits, but also lots of other actions when using a big external monitor.

What should have happened: Performance is the same as with built-in retina screen.