I'm really impressed tbh, images need very little PP and the detail is great. The 9fps came in handy too. One thing I did notice (which has been reported on the D5) is that if the subject is quite small in the frame, is dark/in shadows and the background is very busy the AF can pick up the background rather than the subject. Very rare tbf, and I'm not sure if the D750 would have done the same (I got speaking to a guy with the D810 and he complained of his doing it) and it might have just been the conditions (shaded road with very bright busy background) as the last times I've done the marathon the weather's been a bit pants so not as much dark and light. But I thought it worth mentioning

At 9fps the odd missed shot isn't going to hurt
But overall I'm very happy. I'm just going through the pics now for Arthritis research and I'm really happy with the detail and colours, very pleasing