I've been recently stuck behind AA jets at LAX and JFK taxiing at snail's pace
Add SFO and DEN to the list in the past week or so. To the point in DEN that the controller asked him if he could taxi and faster. Said yes and continued at a snails pace.
We'll know for sure when the start doing transcons at 16,000 as legend would have it at UA during the summer of love.