So everything's in, and while it was a relatively straightforward installation (honestly the only difficult bit was getting the motherboard risers out of the holes appropriate for an ATX board and getting them in the mATX ones. I tried the CPU fan at 100% via the bios and I don't think it's any louder than it was with the water cooler on the old chip.
I'm a bit concerned about CPU temperatures though. I did slip a bit when installing the CPU cooler and the contact patch maybe touched the CPU more than once, and I'm worried that it maybe didn't apply the paste correctly. Granted, each CPU core seems to be reporting the same temperature, and if the paste were missing in some areas I would have thought they'd differ. At the moment it's idling between 50 and 60 degrees, but when I played Borderlands 3 for ten minutes the temperature didn't climb above 75, so it's not like it was bouncing off the thermal throttling mark (although I suspect the system is now very much GPU bound so it may not have been a proper workout). I've tried with the case open and it doesn't vary all that much, so I'm reasonably confident that it's not the new fan config.
Incidentally I can link the motherboard software to my house's hue lights for added RGB control, which is about the most ridiculous feature I can think of for a motherboard. I've not managed to work out how to sync the CPU cooler RGB to the rest of the board yet; it's possible I've used the wrong controller cable (it comes with two). RGB lighting was hardly a priority, but the CPU came with it in the box and the RAM barely cost any more, so I figured I'd go for it in case I change my mind later.