Terry wrote:^^ Very good question Sir
I wish I knew the answer too - so for now I am assuming 100 K.P.H.
However I am sure that I have also seen other higher figures elsewhere.

On my recent visit to Isaan I was stopped by the BIB numerous times and reminded the speed limit was 90KPH.
I stuck rigidly to this on my way home, even setting my SatNav to sound an alarm if I exceeded the limit. When I was stopped this time, the BIB insisted the limit was 80KPH, and I had been doing 110. Mrs BB chewed the poor guy up and spat him all over the motorway when he tried to impose a fine.
Therefore, I guess the speed limit travelling North is 90KPH, and travelling South is 80KPH
One thing I did notice was that when additional restrictions were imposed e.g. 60KPH, there was never a sign indicating the additional restrictions had been removed.
Regarding the mini-bus speeds, yes, I have noticed many of them driving much slower these days.