I guaratee that a D40 with a Nikkor 70-200 VR onboard will blow away a D300 with an 18-200 onboard.
Whilst the 70-200VR is quite rightly a superb lens, its a professional quality lens and its big and cumbersome ( almost 1.5 kg and 215 mm long) and only covers a small range, but, if your ok lugging that around all the time, that would be great. I had a Sigma 70-200 f2.8 for a while. Its 25mm shorter than the Nikon lens, but it was too big for me to use all the time. I would also have needed a bigger bag to carry it in whilst attached to the camera. I sold it.
Also I am sure that the 70-200 iq would be great on a D40, but the camera only processes what the lens sees and I cant believe all the advances in the D300 would be negated just by the use of a lens on an older less sophisticated camera.
But if you get the 70-200, what will you use for closer work? Taking the glass glass glass arguement further, you will need at least 2 more lenses. Say, a 24-70 f2.8 at £1200 and a 14-24 f2.8 at £1000. What about over 300mm? Will it have to be an f2.8 lens?
So, are you going into Nikon ownership as a Pro, needing pro lenses, or do you want a lens/camera combination that you can carry around on holidays / day trips etc.
And, if you do buy the 70-200VR as an investment ( I`m not knocking the lens, I would love one too, but I am practical) what will your ultimate camera be? Full frame or cropped? The latest review from dpreview on the lens suggests it is not too good on a full frame camera (
linky)
I am not saying that I agree or disagree with the "glass first" argument, but, you need to weigh up what sort of photography you will be doing against the cost of doing it.
Then, go buy the D300........
