Aibohphobia
The MSI X99S Gaming 7 has a 3.0 x4 slot but I'm only getting 1400-1500. Is there maybe a newer revision that is faster?

I don't know. With your setup have you verified that the motherboard has it running at PCIe 3.0 speed? Only the slots piped directly into the CPU will use PCIe 3, the X99 chipset is stuck at PCIe 2.0. If you are using a 5820K with the decreased number of PCIe lanes, I have no idea how the routing would be handled either.  
 
Looking at the manual for your board, the M.2 slot has a switch that links it to both the chipset and the CPU slot so I'm not entirely sure how that is supposed to connect and what decides where it switches to. I don't know how it can route to the chipset and remain PCIe 3.0 capable, basically you'd need to find out how that switch works exactly. 
 
Edit: Found a PCIe Bandwidth table later in the manual. Did you enable or disable the "M.2 PCH strap" in your BIOS? Looks like it limits the M.2 to PCIe 2.0 if you have it enabled. With that off and only 1 or 2 GPUs installed then the M.2 slot is supposed to be PCIe 3.0. Installing 3 GPUs will force it to run off the PCH instead. Can't have any drives installed in the SATA 5 or SATA 6 port either.

Ended up selling the drive so I won't be able to test that. I had the M.2 setting in the BIOS set to PCIe.
 
I didn't double-check if it was 3.0 but I had also tested this drive in a M.2 to PCIe x4 adapter and got the same speeds.

Wow so in just one day you test and a day later you sell it?
 
I'd be willing to bet the M.2 to PCIe x4 adapter was 2.0
 
Press release states 2150 / 1550 so I doubt it isn't capable of close to those speeds.
 
Here's an article. http://techgage.com/news/samsung-unveils-first-pcie-3-0-x4-based-m-2-ssd-delivering-speeds-of-over-2gbs/
 

I had it almost two weeks.
 
I used the Bplus M2P4A Adapter. It's listed as 2.0 but if it's just a dumb pass-through adapter I'd think it would operate at 3.0 if in a 3.0 slot. I checked the manual for the MSI and it should've been running in 3.0 mode. I had the setting in the BIOS set to PCIe and there was only one video card installed.
 
I suspect instead that the SM951 drives on eBay are 2.0 AHCI drives. The SSD Review SM951 CES article mentions that there are different variants to cater to different OEM needs. 
 
BTW, here's the numbers I got with the drive in the adapter:
 

NAND chip
 

Well, regardless of if it was your system or a possible PCIe 2.0 "variant", going by your performance data it looks pretty clearly to be bottlenecked by the interface. 
 
The drives only just began mass production, earlier samples probably have a pre-production firmware on them regardless, that also could be limiting it to PCIe 2.0.

So could we see them more widely available around end of February 2015 or later than that?

Well I got my SM951 in on Friday and it is amazingly fast. I think windows 8 installed in around 6-7 minutes.

pakiefarkas
Well I got my SM951 in on Friday and it is amazingly fast. I think windows 8 installed in around 6-7 minutes.

Any benchmark numbers would be appreciated

pakiefarkas
Well I got my SM951 in on Friday and it is amazingly fast. I think windows 8 installed in around 6-7 minutes.

That's about what I got too.
 
What motherboard are you using and is it in a M.2 slot or a PCIe adapter?

pakiefarkas
Well I got my SM951 in on Friday and it is amazingly fast. I think windows 8 installed in around 6-7 minutes.

Windows can be installed in 3 minutes if you use a USB 3.0 install drive (with actual USB 3 drivers added to the install media) and a regular old SATA 3 SSD. A USB 2.0 drive is about 5 minutes. Optical media is closer to ten. It's a poor metric to judge an SSD by!