Totally wrong information from you. You quote a hard drive fact that Hard drives slow down as they fill up which is very true for hard drives as they are rotating mechancial drives which have to change density as they fill up. This has absolutely no relatinoship to SSD's which have no relationship to rotating mechanical drives.
Both SSD drives in your situation will have the same performance and be much, much faster than any hard disk drive
Do not call SSD's a Hard Disk drive, they simply are not.
I wasn't trying to indicate that, I just think of Hard Drives as applying to both. I suppose I should restrict it to "Drives."
I did not know that SSDs worked quite that way.
So, let's change this to the case of an HDD, then.
Percentage VS gigabytes used?
If you exclude Hard drives with their rotating disks then there is absolutely no difference
Each hard drive has different characteristics. As an example here is the Read cperformance with an Seagate ST2000DM001
I did not like the first graphic I posted here is a better one
Notice less than half the performance at the 90% full point
Here is the SSD performsnce responce (It happens to be 3 256 GB Samsung 840 Pro's in RAID 0)
Notice that there is no fall off as the SSD's fill up.