Just a thought, but if you do disable the speed pulse, will the Satnav not be affected too? Or are there 2 sources for the speed pulse?
If you do disable the speed pulse then yes, you will loose GPS accuracy, particualrly in tunnels or in the city. Some of the other hacks do have this side effect.
As this hack does not modify the speed input to the head unit, it does not have this side effect. Rember, to enable the phone and menu system you have to use the soft override via the volume screen.
Kinros