I'm currently investigating nameplates on patch 5.4 ptr.
Default nameplates:
rDiabloPlates enabled:
rDiabloPlates enabled ... everything removed, healthbar texture replaced
So actually I gain fps on the last screenshot. I think the fps drop is not an issue with the nameplate addons in general. I think it has sth to do with how many objects you create etc.
So one has to be very carefully when building nameplate addons. They can eat your fps alive.
Currently investigating all that stuff a little bit more.