I don't think they are trying to imply that "1440p looks bad on a 24 inch screen". What they are implying is that the pixel density is too high at that screen size, and that it might be a better deal to get a bigger screen for that resolution.
I personally don't think that is necessarily true though. If you are only planning to buy one screen then maybe 27inches is the way to go, but if you will buy multiple screens then 24 inch screens might be better since they will be slightly less expensive and look great.
Also forget about Gsync it is a temporary gimmick. New HDMI revisions will support adaptive sync technology natively and it will probably work in both AMD and Nvidia cards.
I see your system specs, so it seems you have money in your pockets... yeah just go with the 27 inch display, but honestly, why don't you just wait for 4K at higher refresh rates? It will come out quite soon.
1440p seems like a temporary transition between 1080p and 4K I really don't think it is a resolution worth upgrading to.
I barely made the jump to 1080p about a year ago lol, but I went from single screen to triple screen, so it is a bigger jump than it seems.
I suggest making upgrades that are more significant.