I checked the Primo version; 9.6.13.405512; so fairly up to date. My previous wince system was Igo8 (8.3?).
I put in an older Irish map (late 2014, early 2015?). The simulation speed on my road dropped to 25kph; the speed limit was not displayed.
When I put back my current map (early to mid 2017) the simulation speed rose to 30kph again. On a narrower nearby road the simulation speed was 25kph in a 50kph limit.
So it seems that Primo 'silently' does not display speed limits for "local" roads, whatever they are; which I find disconcerting and unsatisfactory.
It seems that the simulation speed is taken from the map. It seems to vary from 50% to about 80% (perhaps as high as 90% for motorway). Perhaps it is what is used to generate the arrival time estimate.
All a bit inconclusive, and no nearer to answering my original question. Perhaps it can be re-phrased; how does one get primo to show speed limits on all roads, not just some roads?