I believe the e39 M5 is a 4.9 V8. The e60 M5 is a 5.0 V10, so only 0.1 difference but 107 bhp more. I think I've read somewhere that with a different exhaust and maybe some other things the e39 can also go towards 500 bhp relatively easy. I like the looks of the e39 more than the e60, I wouldn't mind having one in the garage.