Darren, the midrange, tweeter and crossover are the same on all models, the reason for the '70 measurement is it's the only one available. It will be the same for the others.
The new tweeter will indeed most likely sound superb. It will not, and cannot, correct the off axis discrepancy though - that is caused by crossing the midrange dome over at 3.5khz, by which point it is more directional than the HF unit.
As I've said before, this really isn't an issue in the studio where first reflections are well damped so it's not a problem for the intended application - nor anywhere else provided care is taken.
But you have to take your hat off to Harman and their R&D team.