Depends on how close you sit etc.
300 ppi at 11" away. (Retina displays on tablets are this, and why 300dpi on a tablet is good)
Standard sitting at a pc is generally 20-40 inches. 2 and half, to 3 ft. 30-36inches for ideal.
you'd top out at 200ppi visible.
Digital Society Do you really need 300 PPI on a 3.5 inch phone?
math Im seeig here, actually has it even lower. hrm. need to double check my sources when I last discussed this. (had a guy insisting you needed 300ppi monitors to use for Photoshop and professional art. which was beyond idiotic.)
anyway,
3840x2160 on a 22inch monitor is 200ppi.
on 30in, 147ppi.
standard 1920x1200 on a 22 in is only 102ppi.
down to 75ppi on a 30inch
I'm sure most would agree, that is very much visible at comfortable sitting distance.