Right, and thats correct. The 'prediction' service is not auto-complete. Prediction is when you start typing a search in the address bar and it fills in the rest for you. Like, if you went to Google's website and started typing 'I hate when Voldemort' and Google fills in the rest. Thats prediction. Auto complete is when you type 'www.goo' in the address bar and Opera adds the 'gle.com' as you type. They are different things.
I don't really understand... for me, it's the same thing... But leocg said there is no option to disable auto-complete, now I'm sad.
As for your speed dial folder just delete everything inside the folder and it will go away.
I did it several times, the folder is still filling itself like magic everytime I go on a new website. (Only with new websites)