When it comes to gaming, a significant part is the video card. That 550Ti is decent for expected moderate graphic performance, but FFXIV is a rather intense game. Your issue with NPCs lagging out or mobs popping up later is only a graphical thing if everything else is equally lagged. For example, if your character is moving fine, it's likely not a graphics thing. You'll notice graphical problems easily, as it usually involves a lot of stuttering (seems like your screen froze for a second or so). Some exceptions, but yeah... in this case, if your character seems to be fine, it's likely to be lag rather than performance.