Having a hard time deciding how much the A14 vs A12Z difference really matters. The A14 will almost certainly be faster in single core tasks (which is the vast majority of what you do on an iPad) just because it is based on a 2 year newer architecture. But, the current state of iPadOS doesn’t utilize either chip to anything near it’s potential. So, does it even matter? The extra RAM on the Pro might make more of a difference for everyday tasks. But we just won’t know for sure until we have them in hand and can compare.
If you can get by with 64 GB of storage, it’s really hard to recommend the 11” Pro right now. The Air is so close on almost all fronts and I don’t know if a Pro Motion screen and quad speakers are worth $200. You’ll notice I didn’t mention the camera differences because they have the same wide angle lens and I don’t think anyone cares about LIDAR. If you are like me and only need up to 128 GB of storage, then it’s a harder choice. At that point, I would probably spend the extra $50 and get the base Pro over the 256 GB Air. The A12Z will still be plenty powerful and 6 GB of RAM mean the iPad will be more than useable long into the future. If you need more than 256 GB of storage, I would probably stick with the Air.