Thanks Stephen, I've read a few articals that say much the same as you regarding the 1.4 extender, but feel that this will not give me the range I require when on safari.
I could of course take my Sigma 50-500mm with me, but was hoping to travel with just my 24-70mm f/2.8 and the 70-200mm f/2.8 plus extender.
I have already arranged the purchase of the 70-200. So will play with it for a few weeks before deciding on which extender to buy.
Last year when on safari, I reckon 75-80% of my photo's where taken using the 24-70mm as we get very close to most animals. It was just the odd cat/s that required a longer lens, however the amount of very coulorful birds was a different kettle of fish altogether, especially the kingfishers and bee-eaters.
This where I think I need the 400mm that the 2x extender will give me.
I could of course ask my wife to buy me the 100-400 IS lens. I wonder if she will go for that, after all we're only talking approx £2000 for the lot
Harry