Even if the curves were superelevated to the maximum of three inches?
The maximum where you are carrying piggyback or double stacks is usually 4 inches. In the past there were a lot of curves on railroads with 5 and 6 inches superelevation. But, for the most part cars were with the "Plate B" or "Plate C" outlines, which means no more than 15'-1" or 15'-6" high. The top of the top container on a double stack car is 20 feet above the rail.
Passenger only lines, including many transit lines go up to 6 inches superelevation. Some systems will go as high as 180 mm which is right at 7 inches.
Do you mean unbalance? That is the difference between the superelevation that it would take to exactly balance the centrifugal force at the speed limit and the actual superelevation in track? If so, that value
is 3 inches, although with FRA approval up to 4 inches may be allowed. In general 3 inches, which is equivalent to 0.05 g lateral acceleration, is regarded as a reasonable comfort limit for trains since people are not strapped into or otherwise stuck in their seats so they can be and frequently are up and about while the train is moving.
So, for the 3 to 4 inch range of actual superelevation that is commonly used on this line, the passenger speeds will be about what they are now.