RT-AC88U Temps

I picked up a second RT-AC88U to replace my RT-AC66U in ap mode on the lan from ebay for £91

interestingly it runs alot cooler than my release unit

RT-AC88U 2015 Build Date
Bootloader (CFE) 3.0.0.0
Temperatures 2.4 GHz: 47°C - 5 GHz: 51°C - CPU: 73°C

RT-AC88U 2016 Build Date
Bootloader (CFE) 3.0.0.2
Temperatures 2.4 GHz: 47°C - 5 GHz: 51°C - CPU: 66°C

does anyone know if its a case of a better heatsink/paste or a better soc e.g. die shrink

the org one...

RT-AC88U Temps