I have found my 70-300VR to be quite sharp at 300mm. I have tried taking photos at 300 and another at 200, and then cropping the 200 shot to get the same view as at 300. The 300 shot is always better.
Here is a shot I took zoomed right out at 300mm, this was taken with a D3100 by the way.
Here is a shot I took zoomed right out at 300mm, this was taken with a D3100 by the way.