I'd ask other iPad owners for their opinions. I'd also check if other iPad 2 owners have an issue before thinking of an upgrade. You could also consider Android then you could run Tower.
I've got all iPad Minis - first gen, Mini 2, 3 and 4 - and four Android tablets (my son repairs and works on this stuff so I'm stocked with more options available than I need), and my go-to Mini is a 2!
A full-size iPad doesn't seem to perform any differently than it's Mini counterpart, so I'd pretty much lump them together. As long as you're careful to remember to keep
all other apps closed when flying/recording, your video should be optimal. Granted, the Mini 2 only has a gen 6 chip (I think) performance doesn't seem to suffer.
As far as Android tablets go, my choice is a Tab 4. It's small, light, has good video quality, and is cheap enough to keep dedicated for Solo use and kept charged in the backpack with the Mini 2 at all times.
Reading this thread though again reminded me to load the Solo app onto my iPad Pro and see how
that combo rocks the boat!
Not, however, that I'd actually take it out flying. Geez, the size of this puppy!