There are plenty of fast guys in the field. There's 2018 Dubai champ/CR holder Mosinet Geremew, 2017 Boston/World champ Geoffrey Kirui, 2018 Tokyo champ Dickson Chumba, and several more.
But this thread isn't about them. This is about Mo Farah vs. Galen Rupp. Former training partners under Alberto Salazar, Mo left NOP at the end of 2017. Their marathon PRs are 14 seconds apart (2:06:07 for Rupp, 2:06:21 for Farah). They haven't raced since the 2016 Olympics and have never raced in the marathon. And Rupp has only beaten Farah once in 22 head-to-head matchups, and that was in an indoor mile in which Farah fell during the race.
Who finishes higher, and why?
Update: We've published a history looking at the past history between Farah and Rupp: