27" or 24/25" Differences?

Hey Guys, I was set on purchasing either a MSI MAG251RX or the ASUS VG259Q or QM and of course, I can't find one anywhere where I live in Canada. Then, over that time of waiting for stock to come that hasn't btw ;-) I started to think what am I doing. I should buy a 27" screen. I would have been happy with the 1080P display on a 24" monitor but am thinking that the 1440P might just be the way to go. I guess my concern is that I don't want something that would make me feel sick or bother my eyes sitting so closely to it. I would be forced to be roughly 2 feet away from the screen and currently I have a 24" that is fine. Also, my eyes are getting older and yeah. So, what should I do? What would you do? The new monitor would be for gaming and I was looking for a G-Sync capable one. Thanks Guys, Great new site btw.