Basically what I found((as RazberyBandit mentioned) was that if cooler is listed as compatible in lower series cards, it will fit on to the corresponding higher series card. For instance 4870-5870-6870, reference cards of-course.
Only thing to keep an eye out for would be (if your card has a back plate or not) the type of screws included to hold it in place- Knurled, Button-Head, etc.
Edit; and how far they stick out for crossfire.