I use Signal Cable's Silver Resolution.
Whatever you desire, copper, silver etc. Its all about synergy. Stay under 2 Mtrs if you can. I am aware that this TVC can handle up to 5 Mtrs, however my experience was the shorter the better. Low capacitance cable seem to match the TVC.
If you can make your own contact Nick and find out what wire he is using internally. use the same wire.