I agonised over spending so much money for a lens but have since basked in the pleasure I get from using it. It has transformed the quality of the wildlife shots I now get.
The f2.8 and the seamless attchment of the 1.4x II and 2x II extenders makes this a versatile wildlife lens. I love it.
It has increased in price by £1000 in the 18 months I've had it, which is good news for me but bad for my photo-buddy who had been hoping to replace his 100-400.