I have used Clothes Morph by Dimension3D to transfer hundreds of morphs from super hi-resolution figures to super low-resolution versions of the same figure in literally seconds.

Personally I am interested in the medium resolution and low resolution figures. I have rendered Posette well morphed at 4000x4000 with FireFly object smoothing and seen absolutely no resolution artifact. Resolution is better applied to clothing then figures given that even lower resolution figures look just fine nude with render smoothing. My opinion is that the optimal resolution is just only what is required for morphing no more...