The question for the 9.7" Pro is whether it provides enough advantage over the Air 2 to justify the premium price. Apple Pencil (a $100 optional accessory) support seems to be the big advantage, but I suspect that you'd have to merit use of the Pencil outside the airplane to justify the cost. The Pro's screen is also apparently less reflective than the screens on prior iPads, but in my in-store side-by-side comparison with the Air 2, it didn't appear to be drastically so. The improved audio may be important if you have a use case for it, but I'm using headphones most of the time for privacy. The one thing that I didn't care for was Apple's $150 keyboard case accessory, which was just slightly too narrow, with the surface are of the keys just slightly too small, to make prolonged typing comfortable.
I have an iPad 3, so I'm sure that either the Air 2 or Pro would be a huge improvement in speed. I've looked at the mini, but since I use my iPad as a laptop replacement for many things, I'm not sure that the mini would cut it for use outside of the airplane.
JKG