The more I think about it, the more I'm convinced that 39 mm is the perfect size for the Master Control line.
There is a balance at this size which is a bit lost, when you grow in size, in the Master Control line.
As for the Master Grande Tradition Tourbillon, it doesn't have a silicon escapement.
In fact, only 2 of the Master Grande Tradition received a silicon escapement: The Yellow Gold MGT Tourbillon Perpetual Calendar and the YG MR Regulator.
All the others housed a conventional escapement.
Best,
Nicolas.