Back in the day when they ran two 750 drills dad and his cousins doubled the speed on them by swapping sprockets with the theory that half the opening and twice the speed would yield better spacing.  It did work but with a drill better still isn't great.  Still have the drill and that was when the transport disconnect was added.  A few times dad thought he could get by without disengaging to go a very short distance to the next field.  Anything over 9 mph would throw the chain off IIRC.  It seemed to leave shorter skips for sure and when things were good it could look really nice.  In wheat it does seem to be much more consistent when running at higher speeds, typically 7-7.5 mph, which was about what we ran in beans.  When saving seed was over with it got expensive to run drills and the first 15" planter was ordered.  We always talked about the SI belt meters but never invested in them.