As someone looking at how these things are going to play in Macs, I'd like to see a comparison with the iGPU on Intel's 10th-gen Core processors, since that's about what Apple Silicon will be replacing in lower-end (more-affordable) laptops and desktops. I can't figure out how to find that info on the site, though.
It's not quite the same, there's a few differences between a mobile and a laptop/desktop chip, but a tally of how things perform with Metal is here.
Of noteable mention, the A12X is faster than Intel Iris Plus (I believe it's the G7 that came with Ice Lake) (the highest ranked Intel chip on the list).
It's hard to say there because we have Tropico (3) on iPad and iPhone, which calls for 3 GB RAM and an iPhone 6S and up, which would put it at requiring an A9, or any iPad since 2017 (min A9)/any iPad Pro, and Civ 6 (and expansions) which calls for an A10 or above, and those, while not the most modern, are certainly very nice games.
As for how the A12X or A14 would compare with the Intel Iris Xe G7 (Tiger Lake), it's hard to say until we have more benchmarks/leaks, but we've seen the Xe G7 running Shadow of the Tomb Raider from 2016 at 30 fps on low in a crowded area.
WWDC had the dev kits running Shadow of the Tomb Raider at 26-30 fps in an open area on medium.
Edit - Arse did their mini review on the iPad 8, and mentioned that the A12 'may not' be able to handle all 3D games on the app store, so I'll add in a couple more out of curiosity.
Call of Duty Mobile: A9 and up.
Samurai Jack: Presumably A9 and up.
Oceanhorn 2: A10X and up.
Genshin Impact: A8 and up.