There is the technical or scientific aspect to size/distance, a sort of law of variable proportions or law of diminishing returns if you like, no point investing in something that the acuity of the eye and vision can not differentiate or perceive, lots of info on the net to make an informed choice. On the gaming side of things i think it is a personal thing, one size does not necessarily fit all, i use a 24 inch monitor and i have to sit over three feet away for comfortable viewing when gaming.