I imagine it would mostly depend on your face structure and hairline. Longer hair is better for a higher hairline because it obviously covers the masculine "M" shape and is easier to hold in place (meaning it's less likely the wind will ruin your ability to pass). It also helps reduce a wide profile, especially one with a prominent adam's apple.
Short hair, on the other hand, is highly feminizing to an already soft face (see; the forum's own Celestica). If you think you can pull it off, go for it, but it's all about layers and style. GG's with short hair always have "trendy" styles cut in.
Personally, I think it's just safer to keep it long for the time being. I know I always get depressed after a major haircut :/