The Overseas Award is between two who are impossible to separate.
Michael Phelps is the greatest Olympian ever (some say sportsman) who simply must win. Lovely bloke, who spent a lot of time with the BBC.
Usain Bolt put in possibly the greatest sports performances ever seen, obliterating 'Blue Riband' records. He is a massive personality as well. He was the defining memory of Beijing. A true 'fenom.' He simply must win.
There have been four joint awards in 46 years and this year will be another. The two are simply inseparable (If you do bet, check the rules regarding dead heats with your bookie before you bet). As they are inseparable, back Phelps. It is likely Bolt would win it again if he doesn't win this year - running 9.48 in London 2012 for example. Phelps can't lose it and the award maintain 100% credibility, while Bolt could.
But it will likely be a joint award.
EDIT: My mistake here was not researching who decided this award. It was a panel of reporters who were always more likely to side with the bigger attraction. It used to be BBC staff only. You live and learn!