Does anyone have a Sprint Booster on their 550i? I see a lot of people having them on other E60s but cannot specifically say I've seen anyone with a 550.

If it works, where is the best place to get one?

 

Sure it works with the 550i too. However it still does nothing more than increases the throttle response.
The lag problem of the electrically controlled gas pedal is the same in all E60s, generally speaking. I don't know if the newer softwares have any improvements though.

- Antti -