I've heard of this mystical Full Format option (yeah, I still remember how to perform a full format with Windows). I'm doing it now, but I already did something very similar.
UPDATE
Full format didn't do anything.
When using CDM 1000MB *5, the first read result is 80MBs every time. 80/320/100/270/119 is common for the sequential reads.
I think the firmware is broken, but I can't reflash it. You have to use the Mgician to manage fw updates, and I can't reflash the same version.
Until Samsung releases a new fw I'm stuck with this drive...
Unless this is some crazy wear leveling scheme, and nothing is broken at all. Perhaps this is what happens when too much wear occurs on some cells, in which case running the drive for a few days without any static data may help.