Take £15k burning a hole in pocket for a new(ish) car....
Search AutoTrader online for BMW Alpina B3.3 (Non-multitronic version) 0-60 in 3.8 and its a luxury saloon!!
Add proper sport suspension from H&R......(or KW Variant 3 if too harsh a ride on roads)
Secret: AC Schnitzer used to do a Supercharger mod for the M series yielding a very DTM-like level of performance... no longer made but some BMW garages will have one gathering dust somewhere...
Add to Aplina (as if it wasn't tuned enough already)...
Exercise maniacal laughter each time you get in it
Exercise maniacal laughter each time you rinse a Ferrari, Porsche, Lambo, etc...
End up sectioned for laughing all the time at the madness of your vehicle.
(Why anybody would blow £40k on an M3 or £60k on an M5 I don't know.... the Alpina's whip 'em both with only half the horsepower of the new M5)