9MB/s still sounds like an order of magnitude error, most cars and trucks use 250KHz canbus with about 45% utilization being the highest I have seen,
Mercedes run at 500KHz, and a few fords at 1MHz, but your data rate seems to be for a 10MHz canbus with 100% utilisation, to me that is unheard of in vehicles,
Have you looked into basic compression? most of the status inputs, e.g. brake, selected gear, indicators, plus all the other stuff barely ever changes in this context, Its only really fuel, speed and revs that change quickly, So if you recieve the same packet every 50ms but its the same, then build in to your device a way to compress this down to what ID, how many times, and how often, then when it changes record the entire message and continue along
I've got recordings of close to 400 vehicles running trips, when you do that basic compression, utilization falls to under 6% on most.