Hi and thanks for the input!
I wrongly assumed that there are 2 verions of the P20: Pro and Lite. Turns out there is a third, just the P20. This version is only 9mm taller than the OPX, which I think is acceptable. The P20 Pro is 15 mm taller. I'm trying to see a couple of phones in person tomorrow to get a better feel for sizes. By no means do I have small hands, quite the opposite, but I like to comfortable hold and control my phone with one hand.
I didn't include a budget because I assumed that prices would vary quite a bit from country to country. Where I live, the XZ2 Compact goes for ~530 Euro and the OP6 starts at 519 Euro. Let's say my budget is around 550. The P20 pro goes for ~750 Euro.
I won't be doing any gaming, maybe some occasional sudoku, but I like my phone to feel fast with everything I do. Mostly internet/reddit browsing, messaging, navigating and Spotify listening. Why not go for a phone around 300 Euro? Well, I might, if I can find one that feels refined and durable. Feel is important for me (and highly subjective).
Although the minor complaints are stacking up, my OPX is still working so I'm not in too much of a hurry.
Edit 1: replaced bigger with taller