Hey, well you have a choice between a 1080p 120Hz below 5ms response time monitor(Usually aimed at your FPS Hardcore Gamers) and a higher resolution 1440p monitor with 60hz(Officially) and a 5-15ms response.
As you've already said you want colour depth and beauty that kind of kicks the 120Hz TN pannels out. People rave at how the ghosting hurts game play but the way TNs are designed I can wager that you'll notice the lack of colour depth a TN brings compared to a IPS panel first. Also do not look at the response times that companies release with the monitors because most of them are completely fabricated. It's down to you to look at a monitor or read a review to decide if its fast enough. For most people you won't notice the difference between 1-10ms anyway(Some do but most don't).
Now if you were looking at 1080p IPS monitors I would say good luck as there's more of them than calories in the kebab I just ate. Luckily you've set your heart on the higher 1440p ones and I too have recently researched them and found around 3-5 that are the best of the sensible crop. Now you mentioned the Asus PB278Q which is a beautiful monitor and comes in at the top end but there is a problem with it. Its back light pulses which for some people can cause very bad fatigue. Now are you one of these people that will have a problem with this? I don't know. I don't even know if I am and I decided it was risky to go for this monitor when I have no idea if it will cause these problems.
The second and now my top monitor to pick is the Dell U2713HM Ultrasharp. Putting this next to the Asus there is little difference quality wise but there are a few things that could sway you in the direction of the Dell. Firstly it is factory calibrated which will save you a few hundred on doing it yourself so the picture should be excellent out of the box and I hear mostly good reviews on Dells customer service with regards to dead pixels(They replace any monitor on even one dead pixel when I last checked). Also the after coating on the screen is designed for higher glare rooms compared to the Asus so if you game in a bright room this might be a selling point.
Both of these monitors share similar stand mechanics so they can swivel, pivot and go into landscape mode.
There are also a Samsung offering but it seems to be over 200Euros/150Pounds more expensive along side the HP ZR2740w(Very very basic On screen display) both of which are great monitors but due to the price I always go back to the other two.
Now you mentioned one of the many South Korean Monitors that can be brought from EBay, they are great and also importantly cheap monitors. I have not seen a review that says they are not worth it but the main problem is acquiring one that you can guarantee isn't defective. There's about an 80-90% chance you'll get a good one but there could be problems returning one if you do not order through a good supplier. If you are trying to get the most for the lowest price and you're willing to take the chance then go for one of these but make sure you take the time to vet the sellers. Catleap is one of the brands but there are others. The bonus to these monitors is that you can "overclock" the refresh rare to closer to 90-100 Hz but again this is extra work and you may not be able to.
In summary it comes down to whether your willing to take the chance on the Korean monitors as they are definitely good monitors when they arrive without faulty pixels, etc. If my opinion is worth anything go with either the Asus or the Dell depending on the price. Currently they are both the same in Germany and as I do not know if I will get fatigued with the Asus and the fact that the Dell is factory Calibrated I am now about to buy the Dell.
Good luck with the purchase
