I am not an F10 550 owner but I did have the opportunity to drive the Dinan Rep in Northeast 550 yesterday, which was a stage 3 in engine and suspension. From what he stated on his vehicle the stage 4 and 5 is the intercooler and CAI. The software to go with these higher stages will not add more power, but will better calibrate the vehicle to the IC and CAI which will provide increased gains.
I was really surprised as to how linear and fast this vehicle was. Did not feel any turbo lag at all and was a very fast car considering its mass.
I am a little shocked that Dinan does not offer any HFC DP for this car. His 550 did have the axle back system which had a nice tone, but with DP I think this vehicle could be vicious sounding and add more performance.
I was very impressed with the car's performance. I guess the CAI is not out to market yet, but this rep is getting a new 550 and will have stage 4+ components.
For those that are debating the performance upgrades on this particular car, from the time I spent in the car it is well worth it. A sleeper car for sure!