So the best settings that I've found for the the XL2420t are as follows, now bear in mind that these settings do in-fact need to coincide with other settings via the Nvidia Control Panel
So the two settings that I use on a daily basis are:
Profile 1: I use this profile not too often, but when I do I'll use it while playing games such as H1Z1 and CS:GO etc.
(This mode produces more of a blue-tint to your graphics, which is very good (imo) when playing games as it just makes everything pop out a little bit better to be honest).
Profile 2: I use this profile a lot more than the first profile, I just think it's got a more neutral tone and just makes viewing a monitor all the better essentially.
The only thing that changes here is the color options to be honest. But as I said above, this makes the game feel a little softer and has more neutral colours, more traditional colours.
So the settings that I use within Nvidia control panel are as follows:
And finally, I also use a program to help keep my colours locked in, as sometimes you may notice that if you change the colours/brightness within the NCC they tend to change and get reverted when you play a game and they tend to not revert back after you leave that game/full screen program.
So to keep my settings at all times, I use a simple program called: "Color Profile Keeper" which you can find right here:
Hope this helps some of you.