I Can't help thinking a 550i would feel like an M5 compared to any Mondeo, and be a lot cheaper to buy and run.....
The OP says it himself, probably a moment of madness, as already asked, has he tried an M5? Any of them?
I looked over a new Mondeo at the weekend,just because I happened to be at a pub across the road from a Ford dealer , it was nice, sure, but my 15year old e39 felt sooooo much better when I got back into it and to be fair to him,even the salesman said he thought it would, it's a world away from a rep mobile Ford ,as it should be, despite its years, I wonder why the op is thinking of such a huge jump?
If the OP has a thing for speed but wants a drug crazed Wolf in Angry dog clothing then an M5 perhaps is an option but I can't help thinking he's after the wrong car.
An M5 is something I'd expect a 911 owner who's gained a family to opt for not a Fast Mondeo driver to think is his next logical step tbh....