The modification was required by the producer so he could fit the 1st mvmt in the movie.
As for performance, heifetz had a different interpretation from Oistrakh's, there was more a "masculine" quality to it, as shown by higher bow speed and pressure, that gave his interpretation more an external reach.
Oistrakh's reading was more conservative, but his inner power shown through. It was masterful.
Perlman produced great smooth and round sound, although the whole performance didn't break any ground.