If you race muddy gravel races (DK most years, LandRun every year), Di2 gives you flawless shifting no matter what. One year at DK, nobody I talked to who ran cable shifters had full use of their derailleurs by the end -- but I did. For that reason, I think Di2 is worth it. But beyond that . . .

I just measured the clearance as best I can. From the center line of the wheel to the side of the front derailleur measures 20mm. In other words, even a 40mm tire won't fit unless you extend the wheelbase by about an inch -- something I can do, but really don't want to do. Actually, given Trek's claims, that's something I was sure I wouldn't have to do. It's a big reason I chose this bike over others! (And that's why I'm not a happy customer. Did they really expect all their customers to ride this bike without a front derailleur?)