I've only compared the AFS 70-300mm VR against the AF 80-400mm VR at the 300mm focal length and wide open only.
At a distance of about 150 feet and with VR on, I really can't tell the difference between the two.
At close distances of around 12 feet and in full sun I found that the 70-300 lens wasn't happy with VR on at shutter speeds above 1/800 sec. The 80-400 lens had no problem, but that's because it has two VR modes. One mode is VR is on while you half press the shutter release. The 2nd mode is on when the shutter is pressed. I found that mode 2 is better at higher shutter speeds. But close up when there is no movement in the photo the two lenses are comparable.
The 70-300mm lens doesn't like TC's. The auto focus will chatter when the Kenko 1.4X extender is added. The 80-400mm doesn't seem to have a problem with the 1.4X TC. It won't auto focus at all with a 2X TC added.
I like the 70-300mm lens because of it's light weight. It makes a nice lens for walking around in the woods. The disadvantage is it's not 400mm. So I like the 80-400mm lens better. I find with the 1.4X TC at 400mm it's just as sharp or sharper than the AFS 70-200mm VR II with the TC_20E III extender.
I was going to mention how old the AF 80-400mm lens was but Brian beat me to it. I bought mine in May of 2001. The price has only increased by $200 since then.