I got into it with a BMW Alphina B7 the other day. Up to 105mph starting from 70mph, he was at my door and inching ahead steadily. By the time we hit 115, he flew past me. That car has 500/512 and comes in at almost 4900lbs. Once it gets past it's own weight, that fucking thing is a BEAST. He was the one who honked at me and he did the 3 honks to go. The only thing that got me the jump was my downshift to 3rd and power shift into 4th. With my mods, I'm putting down 410/383.
IMO, that M5 is going to eat your lunch.