As you can see I have the D7100 and D500, I'll tell you straight off the D500 kills it...don't waste your time or money on the D7200 when the D500 is now available.
Though, before speaking out of my @$$...why are you looking at a DX Body when you have two (2) FX already?
Several things:
Aircraft photography and some deep space, sports. Curious though. When I had my d7000, a cropped d600 FX/24mp image was better than the cropped d7000 DX/16mp image for subjects, say 7 miles and further away.
But with the d500, it's a 20mb sensor versus the d7200 24mb sensor, so different cropping maxes. Though better ISO abilities on the d500.
For example, this is 2xTC with a 2500 scope (aka 5,000 mm) on an jet about 11 miles away, uncropped on d600 ==>
Aircraft_20160522_5000mmLens (2 of 2)
To you and me that jet is just a speck in the sky looking via eyesight.
For deep space though a 1.4 or 2xTC is good, as you are not going to get "sharp" images anyway, so FX is fine as ISO becomes important with tracking times. A DX would just give me more reach though d7200/24mp sensor may be more optimal. Although the d500/20mp with better ISO may help .. before stacking and all that fun stuff. I'm trying to improve my Jupiter & Saturn images.
I don't have any problems getting close to close aircraft. Sometimes it's larger than my sensor, so FX fits, except for those few times I need a DX because it's not close nor far enough away for optimal FX usage.
Sports. not necessarily the extra "reach" but the D500 FPS, color rendition, improved WB, etc though indoor sports I find the FX just rocks in the low and sporatic lighting events with ISO usually around 6400 for an FX camera. The d500 would have to be 1-2 stops more of 12,800 to 25,600 to match .. I think.
In the one indoor soccer arena my ISO in one sweep across the field can vary from 640 to 6400 on the D600/D750 at f/2.8-640 shutter.
The tracking, et all doesn't matter to me as I'm always focused on one individual anyways so Spot Focus is used. When you get depth of various players I'd rather make the decision than the camera. So the AF system .. i'm sure would be a nice value added but I don't think I need it. Doesn't help with specks in the sky either.
Plus the D7200 is $1,000 less.
But the D500 is cool too with an upcoming $1799 Black Friday special for D500 and OEM grip.
I've tried the d500 a couple times ...
I may just stick with what I have too ... save money.
For the sporadic weddings / events etc I'll still use FX.