In my own test, Opera did list speed dial results in the dropdown - and they even had a little speed dial icon next to them. But I only saw one when I should have seen more, so it doesn't seem to be very good. (That was using the Developer version.)
As far as I can tell, the address bar dropdown seems to list speed dial results mixed in with results from bookmarks and history and whatever else it searches, and there doesn't seem to be a way of controlling just what it lists.