OK, so, gave it a go today. :-)
First impressions were not great. The default Glide64MK2 emulator is the same as the Pi 3 image - if you have the bezels enabled then the screen will just flash. You must disable them to be able to view the screen, and when you do, sadly the performance isn’t any better. There are many visual bugs just not seen on the Pi 4/400.
However, upon switching to the Libretro emulator there’s definitely an improvement. It’s not perfect and you must set it to 320×240 in the Retroarch options, however it did not display the same issues as the Pi 3 image. On the Pi 3 image if you try to make changes within the Retroarch options it will cause the emulator to crash. You can tinker all you like on the Pi 2 image and it’s fine. This is very confusing.
I still feel Batocera could do with more options on the Pi images for N64. Recalbox has way more options to offer a better experience on N64 so it would be nice to see this too on Batocera.