My TV is the brazilian model of the US 900E but they are basically the same.
When I bought my Sony 4k TV I was aware of 1080p 120hz because of the review the Rtings site did on the model.
But I wasn't aware and had no idea that since the panel is faster than 120hz and HDMI 2.0 bandwidth is enough for 1080p 240hz the TV would actually do it.
I'm using a 1080Ti hooked to a Denon x4300w receiver hooked to the TV.
The receiver doesn't mind the high refresh rate and passes it along.
This is really cool for emulation because this mode disables some of the TVs processing (anything beyond 120hz does it) and I believe this would give a lower input lag.
You can run RetroArch in 120hz in 1/2 speed and it's excelent (I do this on my Sony G520 to be able to play at Super resolution 2048x240 at 120hz) and with 240hz you can run at 1/4.
This and run ahead would be a lag killer.
Here's a picture of the TV and UFO test:
