No and haven't driven the 5-series either.
I know the C6 is very good I'm not denying that. My point is that without getting to C6 levels of road comfort the 5-series may get close enough, to the point that its superior perfomance can make a good (and even better in some cases) alternative when it comes to long distance touring.
Furthermore the 5-series can also be playful (if the 1 and 3-series are anything to go by) on twisty roads if you are in the mood.
EDIT My figure for the 520d is 5,1l/100km. Perhaps your figure is for a pre ED 520d?