I am currently using a YS 140 Sport on my DP Ultimate and it is MORE than enough power for the plane. With an 18x6 prop and coolpower 30, this is almost too much engine for the plane. I can tell you that the plane also flies great on a 120FZ. The FZ has quite a bit more power than the older NC, SF, etc. I wouldn't go with a 120 unless it were the newer FZ. For the price, however, I replaced the engine with the 140 Sport since it was just over $400 from central hobbies and has the same power as the 140L on my Goldberg Sukhoi. I use the same prop and fuel and both engines are within a hundred RPM of each other. If you have access to one, however, I would definitely consider going with a 120FZ as it will also fly this plane great and allow you to hover at just over 1/2 throttle.
Ron