Dr. I is just a bit ridiculous. I have many instances of being equal E on merge w/ a DrI, I'll remain straight and level, the Dr I flat turns and is saddled up <200. They're not particularly fast, and turn only marginally better than the other WWI planes... but they do it w/o bleeding any E. I've also noticed that they can use a shallow climb/dive sine wave that seems to make them faster than their listed speed, since they don't seem to bleed E in a shallow climb either...
