I was playing Destiny for a while with you all before I got fibre (I was pretty vocal about it when I got it). To be honest, it works pretty much fine and didn't really seem too unreliable. That was up to 8Mb but was pretty much 4Mb.
Streaming shows in HD was a bit iffy - 1080p was pretty much a no go, but 720p was usually doable. Vita remote play was impossible, however.
BT are planning to cover most people in the country for fibre before too long so I wouldn't be too disheartened. You might find it's available before too long.