Gotta Move it ! !

On the right the e. neglecta is about two years old. This past spring I planted an e. unknown next to it and already they are too close together. So I need to transplant the smaller euc. This e.unknown is now about 7 feet tall so I really hope moving it doesn't kill it. Can anyone give tell me how wide and deep the root ball might be ? Any other tips on transplanting. I've had good success moving eucs in the past but all of them have been smaller than this one.