Geese are big tough birds and the magnum shells do help to bring em down. Lots of layers of warm clothes seems to take away the kick. You can use regular 2 23/4 inch loads if you let em get close enough.
Goose meat is not greasy, that would be tame store bought geese. It is a very rich dark red meat and can be very gamey. I prefer jerky as the marinade I use makes it taste like good beef jerky.
What state are you in?