what travel of forks ror a nail trail?

skyline92

hey, i ride a marin nail trail (08 or 09) and am considering getting some new forks before the summer gets into swing. i currently ride rockshox tora's, i dont know what travel they are set to, and dont know what length the frame is designed to take. but would like as much as i can get away with, obviously withought riskin cracking the frame and messing up the handling. any ideas on what the frame can take?
cheers