IIRC, the build date on mine is early 01, like 03/01 FWIW. Does your 06/00 one have the 5w30 page in the manual?
And I'm curious, what is your oil consumption like and how clean are they under the fill cap? I know when I was shopping around, and from the pictures posted by people doing their valve cover gaskets, the cleanliness range is HUGE! Some are very clean, others disgusting.
One car I looked at, which had been well maintained, but had high mileage was an early build 2000 and it used 1L/1000Km, which I've heard is not uncommon. He, like yourself used nothing but TWS. I've met another couple of M5 owners, one from the GTA, the other, who I consider a friend, and a really good guy, uses Lubro-Moly 10w60. He has an early 2K car as well and it consumes a fair bit, though can't recall exactly how much off the top of my head. The gentleman from the GTA, who's car was, IIRC, a 2001, used less oil. I think 1L/5000Km?
Mine uses 1L/8000Km, which I think is pretty bloody good considering how it is driven. This is with Mobil 1 0w40 in the sump.
Regarding fuel consumption, my other vehicle is an Expedition, so I don't think I need to say any more on that
But I was pleasantly surprised by a hand-calculated 28Mpg average on my trip to the east coast and back in the M5 last year.