When I pull do a compare on these two cards, I see no difference between them other than the starting digit and the second has a "backplate".. 

You are correct. I am not sure if these cards have the plate between the board and the heatsink that the backplates screw into on the backplate models, but the "black edition" is just black and not backplate, otherwise they are the same thing.

EDIT: I believe people here are calling it the midplate. On the SC I just took apart (6173), the backplate directly screws into the midplate. if no backplate exists, I am not sure if they still have the midplate or not. I imagine they do, they just use shorter screws since they dont have to make it through the backplate if it doesnt have one.

Hello,
 
the 08G-P4-5173-KR does not include a backplate and will have some of the LED areas disabled.
 
In terms of performance there is no difference between the two models.