Well my line is 14.4db and that is roughly 350m which makes G.fast pretty crap...
However because they are attaching the G.Fast pods to the old cabinet a g.fast line would be 300m for me.
In regards to which cabinet it will come from it will be the one you are currently connected to, the pods would be standalone further down the line and would have nothing to do with preexisting cabs.
I think its going to be pretty crap for most people. The people who would benefit most, and most likely to pay for it, won't get the benefit much.
I do wonder how BT came to the economic decision about putting nodes next to the cabinet is worth it.
Also what happens if your in a grey area at 300m and order G.fast to get an extra 30Mbps.. then 12 months later they put a node 100m from your house, will they re-route you to the node? Because its going to be a pain in the butt if you're then stuck at 300m because you bought early on.