Harry, just spotted this thread, so am a little late coming to it. I have the 70-200 f2.8 non IS version. I have to agree with Sassan, it is an absolutely brilliant lens. My needs may not be the same as yours but I can assure you that in terms of quality you will be hard pushed to beat this lens, the f2.8 makes it superb and even at that aperture images are pin sharp and the bokeh is sublime.
Checkout the review at
http://www.photozone.de/8Reviews/len...0_28/index.htm
I bought the lens off Ebay I would have liked the IS version but it was just too much for me. However I have to say that I get more keepers fromthis lens than I used to with a 75-300 IS lens I used to have.
I recently added the 1.4 extender, didn't want to reduce the max aperture any more than F4 and frankly with the 1.3x mag factor of my 1DMk2N giving me 260mm equiv +1.4x which made it 364 equiv, it was enough for me. The same test site as above reckon that this is one of the finest extenders giving a hardly discernable loss in quality. However at the end of the day its horses for courses and you may need that extra reach