I second Hermann's and FK's experience. I used the 25-75x zoom exclusively on my ED 82 A, and whenever there was a need to ID something small and distant, the zoom would be set to high magnifications. Of course, it would depend on seeing conditions where the usable limit would be, but over the sea and especially in the mornings and evenings, air is quite often stable enough that even the full 75x could be the optimum. Very rarely would the optimum magnification for an ID be as low as 30x. Granted, the field of view is not very wide, but since the entire field is usable it did not matter that much. It was more an aesthetic handicap than a practical one.
I now have a Swaro ATX 95, which has much wider fields of view for comparable magnifications, but the maximum true field it gives at its minimum of 30x is "only" 20% wider than the Nikon zoom at 25x. It is really nice to have these wider fields in a zoom now, but I doubt it would be that hard for me to go back to the Nikon if needed.
For the Nikon, I also had an 38x wide eyepiece, but really did not use it at all because I tend to use magnifications between 50-75x so much.
Kimmo