bri, you got it backwards buddy. Topping out is when the shock extends to full travel. There is a very audible "clunk", you cannot miss it. It is the result of the shock stopping the downward drop. Generally, this is not considered to be damaging to the shock.
Bottoming out is when the shock is stuffed and the shock stops the upward travel. This is a big no-no and has the potential badly damage or destroy the shock (valve).
Bill, not sure why none of you guys ever top out, here was my setup, I could very easily top my rears on speed bumps, speed humps and especially on the trail:
F: OME 751, OME 107 (never topped the fronts)
R: OME 762 with 1" spacer, OME 108
FWIW, I'm generally not a fast driver on the trail but I don't putz around either. My guess is that a D2 with ACE would allow more drop than a D2 with sways in the rear.