I'm surprised the author doesn't mention backlight strobing, which is another huge upgrade. Kind of hard to describe to people who have never seen it though, as is the case with most of these improvements.
The second and third monitor recommended in the article have 4ms latency, so there's essentially no reason to buy them.
There are good 4k 120hz monitors with strobing for way less than the $2000 mentioned. E.g. the zisworks kit for Samsung U28H750 (first available already in 2017): http://www.zisworks.com/shop.html