The SSD review already tested
the drive, the performance is great: ~1100MB/s read and ~950MB/s write speed. Higher performance numbers are for RAID 0 configuration.
We also have sata express coming soon, some say broadwell other say skylake... but this should give the full bandwidth of pcie lanes to SSDs via sata express.
M.2 was formerly known as NGFF and it's Sata Express in a smaller package. Unfortunately Sata Express has been canned for Intel 9 series chipsets
You can boot off a PCI Express SSD on your average retail motherboard from the Sandy/Ivy Bridge era? Or you need to wait till <whatever comes after Haswell>?
Yup, some Sony ultrabooks come with M.2 SSDs.
Which would be faster (given same capacity and other variables being equal): one PCIe SSD or 2 X SATA SSDs in RAID 0 ?
2 SSDs in Raid 0 can only ever (capped by SATA) deliver a read speed of (550MB/s x2) 1100MB/s same as the Samsung M.2 SSD, and this is Samsung's first generation device.
With new drivers the OS can access a M.2 SSD more effieciently via NVM Express
starting with Win 8.1. NVM Epress is designed for SSDs, Sata was designed for hard disk drives.