I reckon you're down south, or you wouldn't be planting eucalyptus. Paulownia tomentosa (empress tree) can grow up to 15-20 feet its first year, then less each year after that. Develop a round head at 50-80 feet with 5-8 inch leaves, but they can be three feet acroos the first year!
Large purple flowers.
Lots of other fast growers, too.