Like how the 5er is lighter than the A6

If it is, then yes.

Bmer requeste me to do a photoshop with the cs headligts however those dont work, i tried the x6 one and it looks alright. I like this rendering better than the one by huckfeld :P

Not bad.

Karma deserved! Looks good! I especially like what you did with the boot lid.

And how A8 lighter than 7 series!

And TT lighter than Z4!

Is there a source as to how bmw get new 5 series 400kg lighter?

They meant 400 kg lighter than the E70 X5.
The F10 however will be lighter than the E60 and the E60 already is lightest in it's class

I think there is a misunderstanding here. As far as I know there isn't any official source saying anything about the weight of the F10. 400 kg is only mentioned in Foxfire's post. As you can see below he is just pointing out that the new engine will get even lower consumption when it's fitted in to the F10 because it will be much lighter vehicle than the X6.

LOL, didn't think my post would cause such a confusion. As bmer said, I was discussing the new V8tt engine's fuel consumption in next gen 5 series as opposed to the only current BMW that is utilizing it - the X6. It is a given that the weight difference between X6 and 5 will continue to be more than 400 kg when configuring the cars with the same engine.

So how do you guys know for a fact that next 5 series gonna be lighter or same weight as current 5 series if there is no official source?