If you like the idea of a better finished, higher quality car and like the extra toys and exclusivity then fine, pay the extra £100 a month and go for it.
Its a lot of car for £100 a month more. Its nearly double the price of a 330d, list price
Depends what you want in a car really, do you need a car as big as a 6 series? Are you happy with 2 doors? The 330d in the real would will be virtually as quick (given the 6 series is heavier) and will probably handle better too.
If it was me in the same position I'd hang on for the 330d as I wouldnt want anything bigger than a 3 series (and I want 4 doors).......... but that deal is something to think about I guess.........