Hy.
I think you 're a little bit optimistic about the E39's weight. :)
Of course it's depending very much on the optional extras the car is stuffed with.
The real weight of the E39 is 1485kg up to 1830kg, depending on it's gizmos and it's shape ( sedan or estate) . But a proper one, like you would buy is about 1600kg to 1700kg.
http://de.wikipedia.org/wiki/BMW_E39That's even light compared to E60 and F10.
The E46 gained weight compared to the E36, but it's not that much like a 5 Series. :)
the real weight of the E46 is 1360kg up to 1790kg. A normal sedan or coupe will have about 1400 to 1500kg. That's about 150kg more than a E36 has. And the E30 is another 100kg lighter. :)
http://de.wikipedia.org/wiki/BMW_E46So, that says if you want something light buy an old one. :)