Thank you. Regis, coming from you, that is high praise. I debated about a 400 DO; I have been using an old 500 mm IS (the version I) and a 100-400 II, but wanted a prime and less weight. So far so good.
It's a great lens. I got the 400 DO f4 so I could hand hold my shots. I don't like tripods. To each his own.