I recently did the 400$ Dinan upgrade which raised red line in ALL gears 300RPMs and removed the top speed limiter. In addition, they improved the throttle by wire response for the car in regular AND sport mode. Chris Crawford from DINAN also told me that they did something to the throttle something so that the slight "pause" or "hesitation" between shifting has been removed and the "throttle remains open" i dont understand what this means HOWEVER i must say that i am very impressed by the increase "feel" of power and before where i almost ALWAYS bumped up against the rev limiter especially in 1st gear doesnt happen anymore and the car FEELS 10-15% faster at least and NO i do not work for DINAN or getting anything from saying this LOL just telling my feelings and i am definately an enthuiast that loves my M5 immensely!! I would strongly recommend everyone that really loves their car to do this upgrade, which was performed at my local bmw dealer here which does NOT delete ANY part of my warrany. Then, i would appreciate any stories from others that do this upgrade.
I was told that upcoming are cold air intakes, a different differintial in the rear end to produce 30-40 ft/lbs of torque and a light weight clutch. Also they are talking of an exhaust system that will improve sound however they dont expect to get much more HP from this.