For me a matter of sprinting with Farmer's is simple. If I can shrug them by squeezing my lats up causing them to not hit my sides, I can move my legs faster without worrying about hitting my shins or sides on the bars.
In this Video you can see I have no trouble with speed on my heavy farmers
For me, its as soon as I pick them up the sooner I can start moving with them, so for me the Farmers Pick/Deadlift, is more important then the walk itself in the training stages I am in.