Actually, it turned out to be quieter in FSD2 but louder (like 80%) and more annoying (because of the fans speeding up every 30seconds for several minutes when starting a game)!
So, I've gone back to 70% set in FSD2. After gaming, CPU is around 48, GPU 50, RAM 53, which I'm happy enough with.
Of course, I could change the thermal settings to something like 52/52/55 but I still think that will result in the fans running slower in FSD2 and then ramping up when I start gaming. Besides, it's handy having them spin up to 70% when FSD2 boots, because then I can tell it's ready to FTP into, without needing to turn my TV on