It is a good question.
I would suspect that the savings are highly dependant on the space, so that any studies that might exist would be relavant only to a particular location, and not able to be generalized.
Seems like this topic would be a very good subject for a CFD study. However, if you want to take a stab at some rough manual calculations, I would suggest the following approach (I am assuming that you have an actual space that you are interested in):
Measure the temperature at various heights.
Determine the "U" for your walls and roof.
Using the U and the temperature at each height, calculate the heat loss from that "layer".
Repeat the calculation using a uniform temperature.
For extra credit, repeat each calculation with improved roof insulation.
Let us know what you find out. You might even come up with something worthy of publishing yourself.