After working out some quirks I finally got around to test the RX480 full out on LN2. It’s not incredible but not all bad. This specific card was not the best clocker to begin with so I think we can see up to 1800 MHz on a better sample.
The highest validated result was done at 1650/2075 and with tessellation disabled in the driver, see my submission here.
For LN2 overclocking you need a BIOS which has the cold slow issue resolved (or it will lock in a low power state below 0*C), which will be available soon. I used the EVC for voltage control, more info at HWBot forums.