I'll answer my own question!
With Virgin fibre 60MB plan, streaming from UK to US west coast my streaming speeds have increased from 750Kbps (on Orange broadband) to around 1700Kbps! The difference is pretty huge as I have been able to watch in a much higher resolution and its honestly now the same quality as my US cable TV.
Definitely worth changing up to fibre.
Agreed. Since changing to fibre in uk, my viewing experience via slingcatcher in France has bee improved beyond all recognition
However, this time I am experiencing low streaming from about 3pm onwards to the point where I can no longer use the best resolution in slingcatcher. Still great in the morning and early afternoon. Can't understand it