Every version of 40k seems to have its own "benchmark unit" which is a unit with per point effectiveness so high it shine above the rest and becomes corner stone for all new army list to meta against.
In my side of the world that unit in 5th edition was the chaos obliterator. There was a time here the term "9 obliz test" was coined as the standard meta QC for all new list... simply put if you got a new list, you meta it against a list with 9 obliterators; the theory is that if you do well on paper you should be fine, else expect your list to be in a world of hurt when you bring it to the table.
While 6th edition is still new and we will be expecting a lot of new codexes to appear in due time, the flyers rage have since in my opinion made Imperial guard vendetta gunship the new "benchmark unit" in town. Clocking at a mere 140pts arming with 3 twin linked lascanons and 2 heavy bolters, topped with extra armor being standard feature and squadron rule, vendettas is going to rule the unfriendly sky for some time in the dark future.