I just tested a 2017 AT&T iPad and 2018 Wi-Fi iPad side by side (both on iOS 12.3.1). Wifi is so much faster on the 2018 model: ~320Mbps vs ~64Mbps LAN throughput with AC1200 AP. I did test the 2017 on AC1800 router and it did 128Mbps throughput there.Yeah, I think that’s reasonable. A8X does slow down from time to time, and I did just call it “acceptable” earlier in the post. A10 is sometimes noticeably faster. OTOH, I’m not quite as convinced about A9. While you’re not wrong, I’d say A9 maybe is closer to A8X than it is A10. Thus, perhaps I’d rearrange it slightly, like this:
Class 1 (Good): A8X, A9
Class 2 (Better): A10
Class 3 (Excellent): A10X, A11, A12
Class 4 (Outstanding): A12X
But I have no big qualms with your classification either.
In any case, my preferred performance cutoff in an iPad is A10X in 2019, but I think A10 is OK too. Interestingly, I have no major issue with the performance of my 2017 Core m3 MacBook for surfing and business use, and it falls in between A10 and A10X for its multi-core scores, at around 7000. OTOH, I found the 2015 Core m3 MacBook noticeably slower, sometimes annoyingly so, and that MacBook scores closer to A9, at around 4500-4900 or so.
Apart from connectivity, I was surprised at how close performance was for offline content.
I don't really game or do media editing so just tested my usual tasks: app updates, PDF rendering (image-heavy technical manual), loading Excel, opening an 800,000 word EPUB, searching within aforementioned EPUB. Performance was practically identical (bar download times for app updates). These are all tasks that were noticeably slower on the Air 2.
I think the A10 probably switches to the low power cores a lot of times because I've even had some occasions where the A9 finished loading a split second faster.
With that said, no economic sense to go for 2017 A9 iPad when deals abound for the 2018 A10 model.