The only Seagull Ultimate Google comes up with is a Ultimate 46. Guess it's the one.....

The pictures show an Ultimate that is very, very close to the same as my WM Ultimate 40, which is no surprise. About the only difference seems to be a rather overdone top wing attachment for the Seagull. What is significant to your question is the ailerons on the two seem identical. They're narrow strip ailerons.

Strip ailerons aren't the design of choice if you're wanting the plane to hover or 3D. But you'll see for yourself I'm sure.

The Seagull wingspan is only 1" different than the WM, yet the Seagull weight is about 6.5 lbs. My WM weighs 4lb 9 oz. Mine isn't what you'd call a 3D. With an OS46AX on it, the plane is a rocket. With the smallish surfaces, especially the ailerons, when there is no airspeed, control suffers.

I'd say your choice of engines is good. Your model's weight is going to work better with more, not less horsepower. But don't expect to have really good 3D. The weight loading is working against you as are the thin ailerons. There is a reason 3D models have ailerons that're 1/4 to 1/3 the wing area.