Did my first real outing with the new setup (D500 + 500pf) at my favorite birding spot. Being as it's the first time actually using the camera, at this point I can only give initial impressions and a brief highlight between it and my regular birding rig that I've been using for the past few months (1DX2 + 600III). Didn't do any side-by-side shooting, one because I wanted to dedicated the time to the Nikon, and two, it was too blazing hot to carry around 15 lbs of camera gear across my shoulders.
Obvious things out of the way, the weight and bulk of the D500 + 500pf compared to the 1DX2 + 600III is not even comparable, a different dimension in time and space, really. This Nikon lens is just perfect size and weight, handholding it is a dream. The smooth, small diameter barrel is a joy. After a few hours of shooting in 90 degree heat, I came away with no fatigue whatsoever. Naturally, most any camera/lens combo is obviously going to be lighter than what I've been using, so I can't really count this as a negative or a positive against either setup, but after a few years of heavy rigs, this was a nice change.
AF speed and agility: the lens AF's super fast, probably just as nimble as my 600III + 1.4TC. No issues with hunting whatsoever. This is more a comparison between the camera bodies themselves, and seeing that I'm comparing Canon's best to a Nikon APSC body that's almost a 1/4 of the price, I have to say the D500 is a beast. I shot mostly in single point AF-C (AI-Servo). My main takeaway was that the 1-series just had a more urgent, direct feel to the AF when it was grabbing a target; the D500 feels the same, though just a smidge "looser" in aquisition. With the 1DX2 you can feel when the AF locks on target like a clamp, the D500 is not quite as tactile, if that makes any sense. The good thing is, neither camera misses too often...
Where the D500 completely rocks though: Auto-AF and tracking. Wow.
It just magically nails and maintains focus. Complete revelation, I can see what people have been raving about. Canon has Single Point perfected, but they can't touch Nikon in this area.
IQ: amazingly sharp results, with great fine-feather detail. There's a lusciosness and pop to the Nikon photos that the Canon doesn't quite achieve, and I think this is partly due to the lack of AA filter because pics from the Canon can be made similar in post. Getting it right in camera is best though, and this advantage for the Nikon cannot be ignored. But there's a catch...
High ISO noise and IQ... this is where I'm seeing the 1DX2 stomp on the APS-C D500, which I expected. Somewhere b/w ISO 3200 and 6400, the Nikon loses that punchy dimensionality and starts looking more flat, while the Canon just trucks along. I've easily used shots from the 1DX2 at ISO 25600 without hesitation. This is what you expect on an f/5.6 + crop camera setup, and this is the area that is most going to determine which setup I use.
Overall, I completely loved using this camera and the 500pf. I'm happy with the photos, I'm happy with the weight, what more can be said? For the forseeable future, I'll be shooting both setups in tandem.