If you scale a node with a PerspectiveTransform effect on it, the effective resolution of the result will be as if you rendered the node with a 72DPI coordinate system and then stretched and also perspectively transformed the result.

The PerspectiveTransform effect is defined as a pixel effect so any stretching that comes from the effect's parameters should probably result in stretched pixels, but the inherent scaling of the node prior to the effect being applied should probably be honored so that there is less of a jump in resolution when you add and remove a PT effect from a scaled node.

This also shows up in HiDPI situations where nodes in the default scene transform will suddenly appear lower resolution when you add a PT effect due to the fact that it ignores scales in the transform.