i have experienced this maybe similar incident.
my left and right mountings gave way on the way back from Taiping to Putrajaya.
since it was a Sunday late afternoon, and i was already on the PLUS hiway (after Changkat Jering exit), i just continue my drive.
the car was vibrating violently sometimes, and sometimes when the frequency of the engine vibration matches the car vibration, it becomes stable.
so i was travelling like 90-100kmh depending on the vibration, until near the Damansara exit, my DS just gave way, tercabut.. huhu..
anyway, u can use full rubber mountings on the front and rear, and use normal mountings on the left and right.
they may last a bit longer.