Yeah, get them. Braces are the greatest invention ever. I had braces all through sixth form and so did loads of other people at my sixth form (although i did feel relaly self concious about it) but which is better: to feel slightly self concious about a brace - which loads of people have had so won't judge you about it - for a couple of years, OR to feel really self concious about your teeth for the rest of your life??
get the braces!!
i don't think there are any health risks, but function-wise it'd be really difficult to bite properly with an overbite that big , as your teeth don't meet. i would have thought that an overbite of 8mm would qualify for NHS treatment because you can't bite properly with teeth like that - i was talking to my orthodontist a few weeks ago and he said the ideal for an overbite is between 1 and 5mm.
anyway, get braces.