Ok, I've finally got the chance to test the monitor in its non-native resolution.
The first time I tried to set DCS World to 1080p i got horrible red flickering. I then tried it with HDMI and it looks fine.
So it seems non-native resolutions won't work with display port for some reason.
The resolution in 1080p looks OK. It's not overwhelming though. I guess I'm too used to the 4k now. You'll need a lot of antialiasing to get rid of the jaggies, but at the 40" scale this still translates to a blurrier image.
Not because the scaling is particularly blurry... The problem is the pixels are visibly quite large. However, this is a problem you're going to have with any large scale 1080p monitor.
Overall it's a smoothe image though.
Still, it's nothing compared to the fine pixel density at full resolution.