In my own experience even though the speed limit on my road is 60 Km/h it does not alter the simulation speed which always starts at 45Km/h whether I have a valid GPS signal or not. So it seems that iGO chooses this speed itself and it is always a fair bit below the current speed limit. If the speed limit increases so does the simulation speed, but its always less than the speed limit. If there is no speed limit I'm not sure what happens but I suspect iGO would default to its lowest simulation speed. I guess only NNG knows why.

Cheers, Ian