i personally have never driven the m3 you refer to so cant offer an oponion on that ,

But having owned a E39 M5 i could only sing their praises! ... in fact it took buying a E60 M5 to show to me how good the E39 was....in a lot of conditions the older m5 is every bit as fast as its v10 version... interior is equally as nice a place to be and yes they both heavy but ya get used to it after a while

i always keep an eye on the E39 in case something popped up that took my fancy - id happily have another