These are the test that are run over and over again forever.
The speed of a test is much more important in longer-lasting-regression-tests than it is in focused TDD tests used to drive design.
Also, you should take the time to try to get the naming right in these tests, since they will help provide context later on. This, tied with testing-concept-multiple-assertions-per-test allows you to tell stories, which can help fill in context way after-the-fact, which is critical in legacy code.
Noel Rappin talks about them here podcast-rr-185-rails-4-test-prescriptions-with-noel-rappin
He basically says that to get the right kind of speed from them you need to move from a testing-concept-one-assertion-per-test model to something like testing-concept-fast-contexts with testing-concept-multiple-assertions-per-test.