To be fair, it’s not completely deserving of a separate topic. A lot of it is debate about the value of such estimates, which really should have been well established enough already. I for one plan to drop the debate.
@Djonko PPD is a reasonable simplified approximation that can justify more thorough qualitative evaluations. Binocular overlap is yet another discussion, but my own experiences have shown it is much less helpful to improve resolution with VR than with 3D screens. Enough said.