I was planning on upgrading my iPad Air (A7?) to this "new" 2019 iPad, but now I'm reconsidering after reading this thread. I had also considered deciding between the 10.5" Air and the 10.5" Pro. And now I see the 11" is in the Apple refurbished site as well. I don't mind buying refurbished (from Apple) my current iPad Air was bought as a refurb and it's been great although it has been getting noticeably slower lately.
@EugW do you feel like the 11" is worth the price difference of the 10.5" Pro?
I don't know what features and storage you need, but for example:
$469 - 64 GB 10.5" iPad Pro WiFi
$679 - 64 GB 11" iPad Pro WiFi
$599 - 256 GB 10.5" iPad Pro WiFi
$809 - 256 GB 11" iPad Pro WiFi
It seems the price difference is $210. Would I pay the difference?
Yes I probably would. I own the 10.5" iPad Pro, and it runs great, but there are some annoyances. For example, if you want to attach USB accessories to the 10.5" iPad Pro, you need a dongle, and often you also need external power. Just imaging how annoying it must be to have to attach a Lightning to USB 3 Camera Adapter + plug in iPad charger + plug in Lightning cable just to be able to download a file from a more power hungry USB flash drive. On the 11" iPad Pro, all you need is a USB to USB-C adapter ($3 on Amazon) and you're done. The other annoyance is Pencil 1. There is nowhere to put it with the 10.5", and it rolls off the table because it's round. It is also awkward to charge. For the 11", Pencil 2 attaches magnetically to the iPad Pro, and it charges wirelessly, although it's more expensive. Or you can get Logitech Crayon which is even cheaper than Pencil 1.
OTOH, if you don't need external storage or don't need Pencil, then that's not an issue. Furthermore, if you want Smart Keyboard, it's often cheaper for the 10.5" than it is for the 11". I highly recommend the Smart Keyboard.
However, since you already have an Air I might suggest hanging onto it a bit longer and hope they release an update to the 11" iPad Pro before you make a decision. Even if you don't get the 4th generation 11" iPad Pro, the 3rd generation will likely drop in price at that time. The risk though is having to wait a very long time.