Getting it in the right key is pretty vital. One is usually loudest (or at least capable of being loudest) not quite as high as one can go - if you can just make top G as a harmony when someone else has the tune you will probably be loudest about C or D.

It may be worth asking yourself how loud you can shout to encourage your team at your preferred sport. Obviously if you try to sing like that all night you will frazzle your voice and not get a very pretty tone - but it's a question to ask yourself.