There seems to be some confusion between PCIe and SATA Express. They are both quite different.
PCIe (PCI Express). Every modern PC has PCIe. It's a high speed connection for connecting things like a graphics card, and can use up to 16 PCIe generation 3 lanes to get the required performance. To get an SSD to work on this system bus requires a Non-Volatile-Memory (NVM) controller to communicate between the NAND flash layer and the PCIe system bus, and drivers to make it all work.
The RevoDrive 350 uses a proprietary NVM layer called VCA2, and connects to PCIe using 8 PCIe gen 2 lanes, so the max available bandwidth available is 4GB/s.
The NVMe specification should soon make an appearance in SSDs, where all SSD that comply with the specifications should work with a single unified driver. NVMe doesn't use AHCI, so should be far more efficient than SATA Express.
SATA Express, is SATA over PCIe. It still uses the AHCI layer, and at the moment appears to be limited to 2 PCIe Gen 2 lanes, so has a max bandwidth of 1GB/s without overheads. With overheads you can expect around 800MB/s max.
On Intel's soon to be released Z97 chipset, they appear to have combined two SATA 6Gbps ports and added a (keying) connection to achieve SATA Express. This is at the expense (when SATA Express is used) of sacrificing 2 SATA 6Gbps ports.
If SATA Express is not used, then you can use these ports (minus the keying port) to bring the count back up to 6x SATA 6Gbps ports.