I've noticed that the "system disk monthly" script creates big black (empty) gaps inside the forced fill data created by the "consolidate free space" script. Is this normal?
Yes, this is normal. The script will place the MFT and the directories at 30% into the data on the disk, and create zones from the beginning of the disk with files used when booting, files used by the most used programs, regular files, and spacehogs (less important files that take up a lot of space). Between the zones it creates gaps for temporary files. For more information about all the script see Using MyDefrag
I'm under the impressions of a somewhat general slowdown in disk operations
From another posting I see that you have enlarged your first partition, so now the harddisk heads have to travel further between data on the first and second partitions. This equates to lower speed. Make sure all heavily used data is on the first partition. From a speed perspective it is best to have only 1 partition, so MyDefrag can put everything in optimum positions.
What do you think about?
Your numbers look excellent. For more information see Why does MyDefrag not perfectly optimize my disk?