I've been having some issues getting consistent performance out of my Samsung 840 Evo lately. Screenshot
When I first got it back in January (along with the rest of my new rig), I had no problem getting the basemark read/write speeds (540/520 MB/s, 97000/66000 IOPS respectively). But over the last couple months it's been benchmarking more and more often at the levels seen in the screenshot.
I've gone through all of the recommended OS Optimization settings, ran the Samsung Performance Optimization tool, and used the Windows Optimize (SSD version of Defrag) tool. I'm also using the latest Intel Rapid Storage driver provided by my mobo vendor (haven't tried any new versions direct from Intel yet though). But I can no longer get the SSD back up to baseline performance.