Hi.
Having one of each (E34 & E39) I would suggest that you don't expect too much of the E39. IMHO the E34 is more of the driver's car. The E39 is so sophisticated that it feels somewhat boring compared to the E34. The E39 out-performs the E34 in acceleration and lateral g-force, but the E34 is more fun to drive. However, driving the E39 for 996 km in one day without even being tired is also a sign of quality. Getting confused, it is...
I also find that the build quality of my E39 (2001 model) is quite poor.
Have had new Vanos valves fitted. The electrical settings will not stay in place, the telephone (BMW cordless model) has been changed twice but the problem remains. The telephone ariel fell off and I had to buy a new microphone to the handsfree set. There has been a few more minor errors/problems with the car over the 1½ years I have had it
The luggage compartment is smaller that the E34 and there is no 6 cylinder engine sound. The V8 sound is, in my opinion not the same thrill as the straigh six.
Check the gearbox thoroughly. On mine, the third gear is quite "notchy" and I can feel the gearteeth as I engage it. I told the mechanic about it and he told me that I should expect to have a "harder gearbox" on such a performance car compared to the one I usually drive. He was not aware the my other car is a E34 M5.