When you get arma3_x64.exe crash with too many virtual blocks requested it means (most likely) that you have too many roads in the shapefile.

Too many roads means too many shapefile features. Smallest road feature is polyline with 2 vertices, however larger roads can be huge in the vertices count.

It apparently is counted from the terrain data as whole, because smooth iraqi terrains work fine with 9000 road features but rough afghanistan terrain can crash even below 5000.

Good rule of thumb is to keep the road shapefile feature count as low as possible, with smaller terrains this is not an issue but when you do large terrains with huge road networks, you might have to do some hard cutbacks on the road count.