Have you tested the 520? I have tried both the Disk Trucker and the (rim brake) 520 and would have bought the 520 if the LBS were not so greedy (initially they wanted more money for the 2014 520 rim brake than Trek quoted the 2016 520 Disk, I walked away laughing) then, on the 2016 Spring sale they wanted $1150 for the 2014, although I told them that the Randonee on sale would come below $1000.

So I got the Randonee.

But between the Disk Trucker and the 520 Disk, hands down I would go for the 520. Of course, YMMV...