Greetings from Germany. I drive at the moment a F10 550i with a ECU tuning from Noelle Motorsports. For your information, Noelle was the former motor specialist from Alpina. To delete the speed limiter and for 495 hp and 690 nM the DME und CAS moduleshad to be changed. (Vmax now 305 km/h = ca. 190 mph).
End of February I'll get my new M5. On the EMS (Essener Motorshow, a Motorsports fair in Germany) I'd contacts with the tuning companys. 640 hp are at the moment the way to increase the power and to avoid problems with tempratures a.s.o.
1.) Due to this every dealer can detect the tune
2.) I'd no problems with the tuning. But my dealer made a software upgrade and I'd to recode the modules (a service free of charge from Noelle)
3.) No engine light or somehting else
4.) You need 98 octane to feel the power. 91 octan is not high enough (minimum is 95 octan)
5.) I can only speek about the 550i. You have a new car after the tuning. 80 hp more in a M5 is not quantum leap but perceptible
6.) As I wrote above, 640 hp is the best solution - step 1. The maximum her ein Germany is at the moment 740 hp for an ECU tuning
You need DP for that. The DME coding is not breakable with an ECU tuning. You have to change the DME and CAS modules. Not only one tuner in Germany is able to switch of the speed limiter with a software tuning. Only with the DP your VMax will be appr. 310 km/h (so only 5 km/h more without tuning). More is not allowed in Germany due to the speed index of the tires
Hope it was helpful.
P.S.: Sorry, but I speak a famous accent without the slightest english :-)