Comment by seanmcdirmid

I'm pretty sure your 4K is 28 inches, not 27 inches. 4K 27 inch panels don't exist. That still puts you at 157PPI though.

Edit: it looks like 27 inch is really a thing now and not some sort of labelling trick:

    Monitor Size (Diagonal)  Width (approx.) Height (approx.)               Width (Metric) Height (Metric)
    27-inch (26.9" actual) 23.5 inches 13.2 inches 59.7 cm 33.6 cm
    28-inch (27.9" actual) 24.45 inches 13.43 inches 62.09 cm 34.13 cm