Normally for full HD and a 5.1 sound track as well, speeds over 10mps is fine.
Just full HD anything over 8mps is good.
I would recommend you use a wired connection as it's more reliable then WiFi, plus with WiFi there's interference from other devices around the house.
Some people who have had problems it's normally the routers security and parent controls...
If you are new to these boxes, take a look at the T8-S box it very good and now has 16GB of storage. There's also a T8-S plus which has 32GB, check out there reviews on YouTube or droidboxs main site.
Hope this helps you