I don't think there are any hard and fast rules Olympic, but in a 'heavy' it would make sense to select gear down by about 2000agl for the following reasons:
It helps to achieve a stabilised approach by 1000ft (a requirement in many airlines);
It enables the landing checklist to be read;
If you get a gear problem you have a bit of time to decide what you are going to do about it; and
It ensures that you won't get a gear warning (800ft RA in some types).
(I could add that any stowaways will be dropped well clear of the airport and thus avoid embarrassment but that would be in very bad taste!)
At Narita RWY34 you are supposed to have the gear down before crossing the coast (about 4000ft?) to prevent blocks of ice falling on local communities.