Plextor's M6e is the first M.2 socket SSD we have seen, though it's probably more accurate to call it a PCI Express card unless you plan to risk your warranty by removing the contained M.2 device. Either way, it's free of the SATA bus' confinements, affording the M6e more bandwidth than a 2.5" SATA SSD.
The M6e's quoted 770MB/s read and 580MB/s write speeds had us expecting big things in our custom file transfer tests, but the drive didn't deliver with only 280MB/s. The M6S and M6M also disappointed, often struggling to compete with dated products such as the Crucial m4 mSATA and OCZ Vertex 4.
To be fair, perhaps we shouldn't be surprised as the OCZ RevoDrive 350 is rated for up to 1800MB/s and we only get 630MB/s. Maximum throughputs are based on sequential data moving between two drives, not copying on one drive, which at least halves performance since we are both reading and writing.
Disappointment came when we found that the M6e was slower than many SATA SSDs in the single large file copy test, though it was thankfully able to outpace them by a slim margin when working with many smaller files.
In spite of their less-than-stellar file copy performance, Plextor's SSDs crushed our real-world application tests. The M6S and M6M shaved a few seconds off the SanDisk Extreme II's game installation time while the M6e was even faster.
The Microsoft Security Essentials virus scan results were also a high point as the M6S and M6M outpaced all the other SATA SSDs we tested by over 20%. The results are surprising enough that we ran the test several times to confirm.
The synthetic tests didn't reveal anything too unusual, except Atto Disk Benchmark showing particularly strong 1K and 2K data performance for the Plextor drives. Perhaps this is due to their custom firmware, which is what we also attribute to the drives losing little to no performance after being filled.
Plextor's SSDs are fetching a slight price premium with the M6S matching the slightly faster Crucial M550 and the M6e costing almost 80% more than the M6S with only about 30% more performance.
In its PCI Express form, we would pass on the M6e. We would be interested if it were sold as a standalone M.2 socket SSD at a more affordable price. For now, the M6S and M6M offer excellent performance and reliability, putting them among our most preferred SSD choices.