I had and e39 m5 for years. I loved it. It was a fantastic car. The e55 that I have bought recently is much faster but not as engaging as the e39. That said I was stuck in traffic on the m25 and I was very glad of the auto box and not the heavy clutch..
I have to agree with others , having bought one, I think the e55 is awesome. Makes me really think about the value I would get out of spending 50k more to get the current e63. Okay, so the interior etc would be much more modern - obviously, but I believe the e55 to be as fast as I ever need to go in a 4 door.
Get an e55...
Trev