The would of thought the higher recommend speed is not for the TV service, more so you have 80mbps free at all times for the service. It only takes someone else on the house to stick UHD Netflix on and the bravia core will reduce its quality of it can’t maintain 80mbps from the router. That is why I assume they say faster for a ‘optimal’ viewing, words to that effect. 81mbps should be enough for the Pure Stream service, with not network interruptions. It just depends on how much tolerance Sony want to give.It may not require it but their own service recommends a higher speed.
Sony chipsets also have a low buffering zone size too so I would of thought speed about 100mbps wouldnt offer much of a buffer anyway. This is the reason I use a Shield Pro for 100mbps remuxes on my Sony Oleds.
That being said, Sony should include a 1gbps network port, they are so cheap.