I can give you my .02. I came from an e60 545 V8. Was a beautiful car, plenty fast and handled absolutely awesome with the sport package/active roll stabilization. The e60 was 3900 pounds and felt nimble and relatively small for a 5 series. IMO it was the last 5 series you could honestly cross-shop with a 3 series/m3. It does not mean they were completely different types of drives but if you broke it down to the basics, the bottom line is both the e60 and m3 were nimble, fast and you felt like a true sports car. The 5 was nice since it had a nice luxurious feel and was also a great highway cruiser.
The new 5 is just an absolute boat and not even comparable to the current m3. The size difference is too great, the feeling is too drastically different and the power deliver is too drastic different. If you do not mind used a used e60 m5 would be probably my favorite car. Unfortunately when I bought the m3 the m5 had been out of production and I wanted a new car. I was also somewhat wanting a new body style given I had an e60 for years. I still think the e60 looks absolutely amazing in m5 guise.
In short they simply cannot be compared.