I looked long and hard at this lens, but finally decided to go for a 80-200/2.8 telezoom and a 1.4x converter.
That way you loose some IQ at the long end when using the converter, but you have the 2.8 available when needed, and I have a100-400 if I really need longer.
The strong points that I remember from my research are:
1) built like a tank, heavy
2) very sharp and usable wide open
3) Sealed/fixed length when zooming, doesn't act like a dust pump when zooming
4) still very good 140-420/5.6 with a dedicated Sigma 1.4x APO converter
Hope this helps.
