Based on my past subjective measurements with a DK2, which is a similar resolution (960x1080 per eye), I estimate that the 1200x1080 resolution corresponds to a minimum tolerable font size that would be equivalent to 27pt on my 2560x1600 monitor at 3ft. (This is assuming, first, that because the vertical resolutions are the same, the extra horizontal pixels were allocated to peripheral vision; and second, that it's the same the same 2:1:1 pentile style display. If those are full pixels, that drops by a factor sqrt(2) to 19pt.)