I don't think a 550i with just a dinan ECU will be much quicker in a race than an E60 M5. Puttering around town yes it should feel a lot quicker. The M5 has better gearing for racing with its high rpm band, and is about 200lbs lighter, so in a straight line I bet it'd be damn close.If you really like the F10 5 series and want the F10 M5, go for the next best thing in the same class: the F10 550. THEN get the DINAN ECU which will put you at 500hp and 570tq. The hp figure matches the E60 in hp, but with 570tq you should be much quicker for a while.