I did some research on calculating PPI and what is the reason to having a bigger screen with more pixels.
I currently have a Asus 22" TFT V222H (manufactured April 2009) and Achieva Shimian 27" LED QH270 Lite IPS (manufactured mid- 2013).
I wanted to do some comparison between these two monitors because since I have both and many people have 22-24" monitors running at 1080p, I want to show or try to explain what you will be getting with a higher pixel/bigger resolution, But not necessarily DPI or PPI.
First of all the biggest change you will see is SIZE!
Asus coming in around 22" (diagonal measured) vs Achieva at 27" (diagonal measured)
Asus is around 300 Nits vs Achieva around 350-400 nits Depending on where you go
Asus has TFT TN panel vs Achieva is a S-IPS with LED backlighting
Asus has a nice lay out like every other monitor with brightness/contrast/menus/volume(if avil).
Achieva has an On/Off and Brightness and 4 other buttons that do NOTHING!
Response times (this is what you look for when gaming)
Asus has a 5ms response vs the slow Achieva with 6ms (you will be shot and not even know it!)
Gaming computer has 2ms or less!
Asus Matte finish with anit glare VS Achieva Gloss/mirror (looks ugly when light its you from behind)
Both monitors are stuck at 60 Htz. But I did find forums that you could overclock the htz to 75 or 93 with the Achieva.
Asus has HDMI, DVI, and VGA great connectivity because I could hook up my laptop and desktop and another thing and switch from devices I had hooked VS Achieva one (I repeat ONE) dual link DVI. (thick ass cable)
I thought this was the most interesting find of these monitors. Asus monitor = 102.46PPI Achieva monitor = 108.79PPI. Not much difference.
But that is terms of how many pixels are in those inches Asus with 10498pixels and Achieva with 11834 pixels giving us a 1345 more pixels per inch. You might not think that that is a lot considering a 22in panel has 2 million pixels while the Achieva has 3686400 pixels!!! That's crazy!
As far as buying a 1440p monitor, (if you have the money sure why not), but for people that are thinking of buying one, save your money because you must have a strong card that can handle making all these pixels to your screen (any card with 3gb+ ~ 7950, 680, 780) You need at least $400 invested in monitor (used 250-300) and a badass video card that is $250-400 to run these resolutions. Youtube is ever growing with 4k or 1440p content but you must have the bandwidth for all the media. I tried using Keepvid but it doesn't let you download content over 720p resolution. (what gives). So even trying to see the amazing power of the screen is limited to games, and the little content that is online. (Netflix is thinking soon to bring you that 4k). Bottom line I would wait a few more years when prices of everything come down and we have the infrastructure for this resolution. Right now you are just buying a big 27" screen.
I won't talk about price because that is always fluctuating.
********More about this screen review.***********