Anybody who's driven a P100 Sierra Pickup with a Cosworth Engine conversion will tell you what a total waste of time & effort such a project is.
Yes, that M5 project will go quick - very quick -, but, only in a straight line and that's with the DSC etc working overtime. (if they bothered to fit it)
Yes, I've driven a Cosworth powered P100 before anybody asks, it was bloody awful.
A stock Cossie is much the better drive and I'm sure an M5 is no different.
Interesting none the less however!