You are getting into diminishing returns. 30->60 and 60->120 are big steps up, both in terms of smoother motion and enabling better human performance. For example various experiments seem to show that tracking enemies in first person shooters is easier with 120Hz. 240Hz is already in the realm where it's better, but not much better. 1000Hz is probably a pretty marginal improvement. But people pay big bucks for marginal improvements all the time. The audio space does much crazier things for much less tangible improvements