As someone seriously considering the new C-Class Estate, I too would prefer the refinement and quietness of the C350 Saloon over the increased weight penalty and noise intrusion you get with the Estate.
But, as someone with three kids and a dog who makes frequent long trips, I need a load-lugger with the increased power of a V6 engine. Since I also live in London, Ken Livingstone's proposed new Congestion Charge for cars that output more than 225 g/ km of CO2, makes the C320 Estate a default choice over the C350 Estate.
While increased fuel efficiency is also a major factor affecting choice and Blue Efficiency models will offer consumption improvements, direct injection petrol engines will only be preferable to the noise, vibration and harshness you get with a diesel, if they reduce emissions below 225 g/ km.
Do you know what the Blue Efficiency CO2 output is for both the C280 and C350? it would be helpful to know.