Thanks for the feedback Richard. Good to hear that yours is now sorted. That's good service from Sigma (although as you say, it should have been perfect out-of-the-box).
The Tamron 70-200/2.8 (and Nikkor 85/1.8 which I received earlier in the week) are both stunners. I've not had much chance to test them (other than 10 min sessions in the garden under failing light), but I can already tell that they are both special. (The shot above is a 1:1 crop at f3.2!)
Lefty