1) neither will work as "over provisioning"
Essentially over provisioning means, "out of the total amount of space accessible by the controller, let only part of it accessible by the OS (and the rest will be used by the controller for spare sectors)", not using some of the space that the OS can see is totally irrelevant. you need specific tools (by the SSD manufacturer) or hdparm (or similar) to effectively implement an opverprovisioning space, see (examples):
http://www.tech-g.com/2015/06/13/over-provisioning-ssd-in-linux/
https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/over-provisioning-nand-based-ssds-better-endurance-whitepaper.pdf
2) check the COLOURS in the Disk Management view
Black top bar: Unallocated (where you can create EITHER a primary or an extended partition)
Dark Blue top bar: Primary Partition
Light Blue top bar: Logical Volume inside Extended
Light green frame: Extended partition
Light green top bar: Free Space (inside Extended, where you can ONLY create an additional logical volume)
If you prefer, in the first disk ALL space is allocated by the three primary partitions and by the extended one, but inside the extended one you made 2 volumes and there is some free space left "on the right", still within the extended partition, while in the second disk, most of the disk is allocated by 5 primary partitions (either the disk is GPT or as you say Disk Manager is mis-representing the partitions ) , but there is some unallocated space "on the right", outside any partition.
Personally I don't buy that the ext4 volumes/partitions can create a fifth primary partition, there are 4 entries and no more in the MBR partition table, the filesystem used on any partition won't change this, anyway, if you believe that Disk Manager is misrepresenting the situation, you shouldn't use it.
jaclaz