yeah, i think 40 Hz is a pretty safe bet. or if you really want to stay safe and leave the final decision to the mastering engineer you could maybe just use the hicut on the waves lin lowband eq. the lowest band is set to 32 Hz to default. this special eq is supposed to be one of the best for this job.

take a "pro" track you like preferably from a cd/good vinyl setup (cartridges) as a reference, i wouldn't advise mp3s for referncing if avoidable.