Redubbing is a good idea, at least some characters can be pushed or saved, with right dialog we could get more out of the poor films Lucas made ...
Not very serious, but as examples on how a "proto-Vader" could sound, say if Anakin just had a mask or breathing apparatus (on Mustafa):
http://www.youtube.com/watch?v=ArmRCTKxTeo
or with more temper ... (bad language!)
http://www.youtube.com/watch?v=xh3Wveg4DMk
http://www.youtube.com/watch?v=q_n8FRILoYE
hm, if we leave "the duel" at Mustafa onscreen, I would like to add breathing masks to both Obi-Wan and Anakin, to make it look like in the concept art of McQuarrie ;-)
http://spinoff.comicbookresources.com/wp-content/uploads/2012/03/star-wars-mcquarrie4.jpg