I have had the opposite problem… I had a Samsung 840 (not EVO, Not Pro) and it slowed down over time… It was as if trim wasn’t working… I did get it to speed up for a whle by copying everything off, erasing everything, and copying it all back…THEN it workes fast (I’m talkiing about the Samsung 840)… But over time it started slowing down again… I contacted Samsung and they say it doesn’t do that… but my tests say it does… This Samsung SSD is now relagated to exterenal USB Drive Use…
That’s why I jumped ship and went with SanDisk Ultra II… I have 4 of them now… a 960 in Laptop, 2x480’s in a Raid 0 array, and a 240 being used as a database cache drive. SO FAR, all is fine!!! 
