Well everyone, I started this thread nearly 3 months ago and based on the strong recommendation to go f/2.8 I splurged and bought the Nikon 70-200 f/2.8 VR II with my new D750. I'm absolutely astonished at this combination - I couldn't be happier with the results. Speed, accuracy, detail ... I could go on and on!! Yes, I could have saved significant money by getting the f/4 lens, but the results at f/2.8 are more than worth the extra I spent, and also very useful shooting sports in not so great lighting. I won't splurge as much on a 24-70 - for that, I'll most likely get the Tamron f/2.8.