Common, nobody for the Imperial mail? Mumbai Kolkata route was probably the most important commercial route of its time[~100 years ago] and this train service[one of the most luxurious] ran right through it. It wouldn't be an hyperbole to call it probably the most important train running in its time. So, just for its historical value, I had go with the Imperial Mail[in AC coaches only].
An actual order could be-> Duronto> Super Deluxe