The Leaf product data sheet says they support both your cameras. But I would send an e-mail to both Leaf and Mamiya for any specifics.
Here is the data sheet...
http://www.leaf-photography.com/imgs...f_aptus_ds.pdf
And personally I would not expect the same thing from a Canon 40d. Take a look at some of these...
Best of 2007
And there are many discussions out there on the comparisons of medium format digital backs as compared to the 35mm digital format.