aren't they both 7's? maybe they had to make the malavita highback stiffer to accomodate the heel hammock better? If people ride their straps looser because of the hammock, maybe they need a stiffer highback to offset it.
but whatever, I think both bindings do the same thing
According to their site.
Restricted Maltiva EST: 7
Maltiva EST: 6
Restricted Cartel EST: 7
Cartel EST: 7
Just for discussion sake they list the Genesis EST as 7.