Originally posted by Ian
Your welcome, it's not the first time I've had to put that info down here and no doubt it won't be the last time.
Now to answer your question regarding the differences.
The differences are quite apparent when you look at enlargments in the size range of 10" x 12" where the ED version shows better image sharpness and higher colour fidelity and contrast.
My main gripe with the G series 70-300 is that it's just too damn light for use on heavy professional bodies like the F4 and F5. In this situation it doesn't point well at all and is prone to vibration related isssues. However on a lighter body it seems fine.
Build wise the the older ED version is considerably superior to the G series.