Why don't you try the TomTom (for iGO) maps?
In my experience, they are more accurate. Not only speedlimits, but also routing is better in my opinion.
About the routing: I use TT since some years because (and this was for sure true at the time) the Navteq (now named HERE) made me do unneeded detours, instead of just taking the road I had to take to make my route. (e.g. drive on for a distance to turn back and make the turn in to the street I passed before).
I then "accused" the IGO build as the cause, but replacing that build did not make a difference. Simply replacing the maps did, whatever IGO build. Since I am a fan of TomTom maps for IGO/Primo
You will lack the driver alerts, but keeping the eyes on the road has the same result