I gotta agree with you, I almost bought an 03' M5 and have driven a friends modded e60 M5 and honestly the E60 does nothing for me, thought it was borring/missing something. I didn't care how much quicker it was at high speeds, it was missing this raw like character the e39 had.

I've always like the ol' e34 M5.

 

E36 M3 would be a better DD. E34 M5 and E24 M6 are more like collector's car and require high maintain.

 

I own an E34 M5 and as much as I love the old-school factor (like a 993 compared to the 996/997 generations) it's a bit harder to drive as a DD. Clutch is heavy if it hasn't been changed to a newer one, gearing is optimized for high speeds. It has a terrific sound to it that's addictive though. I drive it once-twice per week and let my Mini handle the DD routine.

I voted for an E36 M3 as the best DD to complement your E39 beast.