So after going through these possible resolutions, the most reasonable upper bound for human vision is the .5 arcminutes value, as while there is a clear increase in detail going from ~300 PPI to ~400 PPI in mobile displays, it is highly unlikely that any display manufacturer can make a relatively large display with a resolution that corresponds to 1800 PPD at 12 inches away for mass production. However, for the .5 arcminute value, at a distance 12 inches away from the eye, this would mean a pixel density of around 600 PPI.
That’s 600 ppi with a RGB stripe sub-pixel format. The Samsung Galaxy S5 is rumored to sport a 5.25-inch 2560×1440 LCD. The resolution? 560 ppi. If the rumor turns out to be true, the Galaxy S5 display in terms of resolution will be very close to the upper limits of human vision.