Resolution over viewing distance ratio

i am interested in decreasing render resolutions along increasing viewing distances.
how are optimum resolution/distance ratios determined ?

optimum ratios meaning, for a constant resolution, a distance
not too close (bulky pixels, like watching a 4m wide projection from 1m away)
nor too far (loosing details, like one single pixel on your display no longer visible after n meters)

found this link optimum hdtv viewing distance
hopefully i will get into actually testing ratios for beamers …