OK
Let's take the far right of the graph on Slush or less than 12.33 times the difficulty.
My bet is 'the round will be less than that' = less than 38587637235 shares
EDIT: It's late evening here so don't trust my maths, but that should be 1/4 of the percent (0.25%) that I am wrong
The far right limit of CDF (i.e. infinity) 
Let's take the far right of the graph on Slush or less than 12.33 times the difficulty.
My bet is 'the round will be less than that' = less than 38587637235 shares
EDIT: It's late evening here so don't trust my maths, but that should be 1/4 of the percent (0.25%) that I am wrong