Welcome to the Green side, please check out our Way of The Waagh thread and join in.
Since you now have the FaQ there is also a little sentence in there showing that even if they stop your roller wagon they still take 2D6 hits. This is important, especially when D'R'ing space marine dreadnoughts.
Now go to the main rule book and find the section where it covers ramming against walkers and mark that page.
It seems that SM players take it WAY too personal when you krump their Bjorn or Furuso dreads. The DR will kill a dread easily, especially when you cause damage to their rear armor value because it death or gloried.
I have had to "discuss" this with many SM players over and over as they watch their dreads get destroyed. Sure they may stop your DR wagon but they still take 2D6 strength 10 hits, which will destroy them as they auto glance and even if you roll 1's you penetrate.
And while you are drooling over the prospect of killing dreads, model something up to celebrate, and enter the: