I loaded my current 196 turn game onto my 2017 9.7" iPad and switched between Retina on and off and took some screen shots for comparison. Fonts are slightly clearer with Retina on, but other than that I really didn't notice much difference. If turning Retina on increases battery drain or heat build-up it's not worth having it on on both of my iPads. YMMV. I didn't adjust ui scale on my 9.7" iPad as I didn't want to pair a bluetooth keyboard to access the debug menu and I suspect reducing the size of the UI elements on the 9.7" screen would make them too small for practical use. I've only experimented a little bit with the game on my 9.7" iPad so I can't really make a valid comparison. It's summer where I am so I ran an extension lead into my gazebo and spent a couple of evenings sitting in my garden playing the game late into the night with the iPad Pro plugged in to mains power. I've no idea if that has an impact on the batteries 400-500 cycle life. The Pro has not noticeably heated up during those long sessions.