No such thing as "Gogeta" as he does not exist in the original manga. However for the sake of arguments, I'm going to finalize why their the same strength, and theoretically speaking Gogeta might be superior in terms of power and speed. Firstly, the fusees in the movies are far superior than their regular selves in the mangas, as evidence that Goku is stronger in his SSJ3 form than SSJ3 Gotenks and Mystic Gohan, evidence movie 13 against Hirudegarn, which Goku destroyed completely by himself, but was defeated by Janemba. Therefore that means Super Janemba is far stronger than Hirudegarn who in turn is stronger than Gohan and Gotenks, meaning that Hirudegarn would have to be around the strength of Gotenks Buu.