Compared to unit tests where the concept of the user doesn't even exist or needs to be shimmed in with a proxy object, I really don't think the user differences

Compared to unit tests where the concept of the user doesn't even exist or needs to be shimmed in with a proxy object, I really don't think the user differences in ACL are the deciding factor between the two. As for programmer productivity, proper parallelization of these tests results in sub second test suite runtime. Maybe more if there is a new dependency that the testing servers need to install, but it really isn't that bad.