As pic shows, on Makemkv my device could only run on 9M/s or approximately 2x. Wonder if there are any settings on read out limit or it's hard wired in the software.
I have found it rare that MakeMKV can run at the maximum speed of a drive, which is what the "6X" or other speed lists. You will see the max as it reaches the outer diameter of the disk, not early on, because the density of data packed into a rotation of the disk changes. Well, check that - the density stays the same, but how much data is on a rotation changes, because they're more disk to go by each rotation.