I’m in the same boat as you, I am still rocking my Bolt v1. I’d start with the question: What features do you really need? In my case, I want color maps e. g. to distinguish between lakes and forests (I moved to an area with lots of lakes). I want 6 data fields when using maps. That’s about it. Due to a distinct lack of mountains and even hills, climb features are useless.
So any modern headunit will work for me. I’d also like 15+ hours of battery life, so weirdly that’d exclude the new 850 and 550, but still leave the 840 and 540 as options.
The only reason why I’d hesitate to switch away from Wahoo is the zoom feature, which I really, really love. It is what attracted me to the Bolt in the first place.