Ok i just got this yesterday, its the 512 gb one.
I tested AS SSD, it is 1000 MB read and 960mb write, as it should be.
Now, im happy as farts and started installing stuff to it, Steam games, Sony vegas, etc, like this for one day, roughly 55 GB of data on it.
I tried AS SSD, and to my horror it's down to 850 MB read, 750 MB write, im like oh crap oh crap now what?
i moved everything off of it and retested it, performance is good as new, THEN i moved everything back...