So now the next question; 70/200 f/4.0 + 1.4x extender or the (rhaa, heavy) 100/400 ?
If you're considering the 100-400 then I personally would pay a little more and go for the 70-200 f2.8 IS
L. This will take both extenders.
I owned a 100-400 and the 70-200 f4 but sold them both. The 70-200 f4 is a lovely compact and light lens. Great for traveling and produces excellent results with the 1.4x extender. I thought the 100-400 was superb until I went digital and then I thought it was "just" good. I sold them both and bought the 70-200f2.8 and a prime 300mm.
The 70-200 f2.8 is a superb lens and with and without the 1.4x extender produces fantastic results. I tend not to use it with the 2x extender as I use the prime for this range, but with this combination it's pretty close to the 100-400.
The 70-200 f2.8 IS
is heavier than the 100-400, but it really isn't a problem to hand hold either of them.