There's at the moment no way to shortcut that, other than overriding RollbackFields in a partial class of CommonEntityBase and setting the byte array fields to null before calling the base' method. that way it will be reported as changed, but the check will be very quick.
Looking at the code, it could be a bit more clever as in: it could check whether the original field had its IsChanged flag set. If both version don't have their IsChanged flag set, they can't be changed, so it can skip the check. Currently it checks the values of byte arrays and ignores the IsChanged flag so it's the worst case scenario: long arrays are compared and they're equal so it will take O(n).
We'll look into speeding this up in the future.