IMO, the problem with running a 12:40 flat pace is that whoever will be in the front pushing that pace is unlikely to win. So basically sacrificing himself. No one wants to do that in a WC final.
And the problem with running over 12:50, is that Jakob will likely squeeze them all in the last k.
IMO, there's a fine line where they should run around 12:45-12:50 for the first 3k, and then push the last 2k at 12:40 pace, preventing Jakob to completely control the last k, while not burning themselves out for the last 400.