Current street DSLAMs can be anything from 3m to upto 100m (usually 50m or less due to planning rules), now the G.Fast pods are being attached literally to the side of the PCP shells there is no neeed for massive tie cables feeding the cabinet in essence there will just be a jumper wire around one metre long into the G.Fast termination. So if your 150m from the PCP and an extra 50m to the FTTC cabinet (totalling 200m line length) then with G.Fast that'll be 150m as it'll be attached directly to the PCP.
not sure what you mean by your area -- if you mean your exchange that means Openreach will deploy to those cabinets in the exchange that meet the commercial criteria for deployment of GFast -- don't assume that all cabs (that are enabled) will meet the commercial criteria of Gfast) as that is most unlikely to be the case