Rebuilt engines should run like new considering there are no parts that are badly damaged or worn. All a rebuild usually consists of is new seals, gaskets, piston rings and a good cleaning.
You really can't say it's a new engine, though-just newly rebuilt. The parts are still worn from mileage.
I got my engine rebuilt (didn't have the balls to do it myself the first time) before I was deployed. They told me to put 1,000 miles of easy driving on it to break it in, so I drove 1k miles in three days and got to have some good fun for about a week before I left.
Jake
from Al Udeid AFB, Qatar