I think a broadhead is mandatory (but be very careful if using a dog to retrieve) unless you are trying to break a wing and then deal with it on the ground.
In my experience, full fletched flu flus, although they sound great, run out of steam well before they get to the goose and are nearly worthless then. Either cut them way back, or maybe make some arrows using 5.5 " four fletch or some other similar bigger fletch.
They need to be close, and preferably nearing touch down so they are not moving as fast. Near the end, maybe the last 10 - 20 feet, they are almost floating down to the ground, and going slowly.
Good luck