The sub-1:40 because it's the only one that probably could already have been broken. I suspect that Rudisha in 2012 could have broken 1:40 if the London Olympic finals had been a time trial with pacers. So all it takes is another Rudisha-like talent and the right race conditions. After that I actually think the 10000m is most likely and the 1500m least likely because the new shoes help more in longer races.