OK – after lots of testing, seems like it’s easiest to animate in after effects, export as a FULL RES .mov and then import MOVIE to LAYERS in photoshop. It automatically sets the frame delay to 0.04 based on 24fps. Keep this delay, as no DELAY seems to output slow play back.
Seems like a lot of hoops to jump through but if you want a bit of control and acurate colour, this is the best workflow.
So, best practice would be to animate full HD RES and reduce size on a FINAL COMP in AE, rather than working to size throughout