It's called steady-state testing, and yes all drives* lose performance if you give them enough work.
To reach steady-state, you have to really hammer an SSD in a completely unrealistic way that is unlikely to ever happen in everyday consumer use.
1) You have to fill the drive so that there are no available pages/blocks left to write to.
2) You have to then torture the drive by continually writing to it before it has a chance to run any internal defrag or garbage-collection.
3) You have to keep torturing the drive to maintain the steady-state, because if you give it chance to stop writing, it will defrag, TRIM and garbage-collect, restoring performance to much better levels.
Basically, all consumer SSD's will slow down from their typical write speeds if you dump tens of gigs of data on it on in one go, at speeds faster than it can write.
In a consumer situation you're unlikely to be able to do this because you need either 10GigE network, another SSD to read from, or a multi-spindle RAID array to stress an SSD hard enough.
* - Intel's current-gen enterprise drives are targetted towards steady-state performance. They are also more than twice the price of the best consumer drives, so it's not even a valid comparison.
This is my signature. There are many like it, but this one is mine. However, my signature is neither my best friend, nor is it my life. I also have no desire to master it and my worth is not signature-dependent.