You should burn at the speed with the lowest error ratio - generally the slowest.
In the battle for speed manufacturers may have forgotten that what is burned also should be burned as error free as possible.
Any CD/DVD has thousands of errors and about a third of the disc is reserved for ECC. When/if the number of errors get too high all can't be repaired
This goes for factory made CD/DVD discs as well
Don't fix it if it ain't broken, don't break it if you can't fix it