I have an E39 M5 -

What they dont tell you - the thing drinks oil like a two stroke, and the ealry cars are way worse than the new ones! I think that the changeover year was 2000. Rumor has it that the later cars has a different piston ring design. All I know is that the 2001 and newer seem to do far more sensible than mine!

The post 2000 have the nicer headlights and the rear lights, wihch make it look nicer.

go for the one with the sat nav system - can be retrofitted, but worth it! If poss, get one with widescreen sat nav, though this can be very easily retrofitted

JJ