I haven't directly compared the two units Terry, but I'd suspect that the additional sound deadening in the D4 would affect the listening experience and possibly account for some of the difference.
From the D4's I've driven, the D4 seems more refined, handles a bit better and feels a bit more upmarket. I far prefer the centre stack of the D3 and my V8 motor to the TD ones I've driven. I've not driven a D4 V8, but I imagine it would be like mine ... but better ... and faster .... :cool:

