Adding 200# to the front of a nose heavy car is counterproductive. Unless 1/4 mile is your poison.
At that rate, just buy an SL55, bolt on go fast parts and enjoy! To each their own. V8 SRT would be fun, OTOH.
you would think the v8/200# as you say would make a big difference ,,it doesn't ,,as the slk/crossfire was overbuilt so, you should drive a v8 crossfire . as mine has been on the tail of the dragon, every Oct. for the last few years,in fact last year a Porsche could not stay with me. if u went with a super charged v8 you would NEVER go back jim