Not sure if I've topped 27. But I can easily get 26.5-26.8 on my 4.0 tune with the aggressive throttle mapping. On my older 3.x tune, I top out in the 25s. Been running them for about 7k miles, mostly city driving. No issues as all.
As others will mention, I wouldn't worry too much. Stratified isn't looking to damage any motors.