Thanks both!
The display is one of the things making me want to try the 12.9" 
While the one on the 11" is great (and certainly black levels aren’t an issue at all) the two things I am not so keen on is:
- Viewing angle. If you’re not looking at it straight on (so eg when it’s flat on a desk) the furthest part of the display is darker/greyer
- Brightness. I’m finding it needs to be at least 75% brightness to be useable, but that could be because my LG 5K monitor is very bright and I may just need my eyes to adjust/dim that a bit.
From what I’ve heard from youtubers both of these might be less of an issue with the mini-led display.
This is another reason why I am thinking about the 12.9" - I found sidecar quite useful with the 11" but it’s a tad small for anything other than YouTube vids. The 12.9" would be much more useful imo. I won’t be taking the iPad anywhere I wouldn’t be taking my laptop, so I’m not too bothered by the 11" being more portable.
I do like the 11"… but I might wait a week then order the 12.9" just to see which one I prefer… or maybe even wait until next year as the 11" will probably have a mini-led screen and apparently they are getting MagSafe chargers with a glass back which would be nice to have…