For one thing, we tend to look at these things in terms of the Imperial measuring system, whereas Cira (designed by an Italian) was probably designed according to the metric system.
I doubt it's coincidence that the original height of 656' was exactly 200m.
Regardless, I can see wanting a milestone height for a city's new tallest, but when it comes to a building that will place 7th in the skyline, the height is really just a number. I can see maybe wanting to do a nice round # of storeys (like 50, as opposed to 49), but 700 vs 690? Irrelevant to an architect.
If it makes you feel better, consider this: on paper, 690' will be a more even spread between the 739' BA Tower and the 625' IBX. The only way I'd prefer 700' over 690' would be if it meant making the crown's peak on the eastern side a bit higher and more pronounced (assuming we're getting a roofline that slopes up as it heads east, rather than bowing up in the middle and back down to the same height it is on the west.)
In any case, whether it's 690' or 700' - 59 storeys or 60 - this tower is going to look AMAZING, especially at that location. Celebrate!