Thanks for the reply teejuk.
Sorry in advance for the following long post!
I actually bought 4 new BFA connectors yesterday for less than £10.00 total and had some 1.5mm diameter copper cable, real cheap stuff (about £1.00 a metre) that I bought a while back for an emergency. I've changed over to that today. Not sure if its psychoacoustics or a real change but I think the system sounds better. The high frequencies have been tamed a lot, no harshness from any track I've played but most of the sparkle is still there. Bass is a bit better. But instead of trying to isolate small changes that I have to concentrate to hear I've just let the music play and see how I feel. The overall tonality and realism is better. A few but subtle parts of music have come through that I've not noticed before. The music is not 'In your face' like it was sometimes, so a little excitement has been lost but with the bonus of more overall enjoyment!
From my experimenting today, having used my existing system for many, many hours with Chord Rumour 2 (silver coated) and today for maybe 6 hours with cheap cable (pure copper), I can say that for me pure copper is better. I can also see why someone may like silver coated.
Speaker cables are worth experimenting with, but I would advise those who want to to compare silver coated to pure copper, maybe 2 of each to start with and see what you prefer.