Soldato
I can only comment on my M135i - but the acceleration/performance is staggering, especially when you consider that it can be relatively economical over longer drives while not costing the world to run.
The rate at which it gathers speed is truly staggering, I would hate to think what a proper supercar feels like with twice the power!!
My favourite thing is when you floor it from a roundabout and you get to the *ahem* legal speed limit (read 100+) and you snap off the throttle - the lack of acceleration throws you forward quite rapidly
There are no new ones left though, I got ours in March last year when they were all built and BMW were giving £12k off them, so worked out about £29.000 each - which is around the same as a Mini F56 JCW, which we had before, and the running costs are about the same, in fact the JCW got less MPG than the M140i (though less pops and bangs than the Bimmer)