I have the Force FX lightsabers of:
Anakin Skywalker E3
Darth Vader E5 (I think)
I think I saved the boxes in my storage, but I keep the lightsabers on display and accessable here at home (love them, as a matter of fact - and I also own Luke's E6 and Darth Maul's double blades).
I've seen examples of how the scaled replicas and LE's are different between the movies because the props varied, but the FXs (my personal favorites) are altered as it is, to accomodate the FX blade and electronics.
I don't think there's much room to retool these for the very small differences in the sabers between films (due to the need for new props when they shot the movies no less).
The Vader seems to have less clash sounds than the others (but more swinging sounds) - and I don't know if this is standard between E5 and E6 Vaders, or even if there is / was an E3 Vader and that is what I actually have.
What has MR actually made in Force FX?
E2 Yoda (is it from AOTC or ROTS?)
E3 Mace (or is it E2: AOTC?)
E3 Obi-Wan (A New Hope style)
E4 Vader (NEW)
E4 Luke (NEW)
E5 Luke (first one, I believe)
E6 Luke (ROTJ saber)
E6 Vader ???
I never fail to mention the need for an E1 Obi-Wan (my all-time favorite lightsaber!)
So what if anything is the difference with E4 Lightsabers other than packaging?