Hi,
I have one EP1, which is similar to a Kingston HyperX Predator (PCIe Gen2x4 SSD using AHCI standard, M.2 2280 form factor).
On the below is CDM test result when I installed it on my PC (i7-2600K + ASUS P8P67 LE).
Here are the problems:
(1) Bad random 4KB QD32 performance
The performance of sequential read / write is reasonable since I’m using an adapter card on PCIE_X16_2 which linked to PCH and only work at x2 due to there is another USB 3.0 card sharing bandwidth.
However, the performance of random 4KB QD32 is far from expected, even much worse than my SATA SSD.
Also, when I changed the setting from QD32 T1 to QD32 T3 or higher, the system freezes during test and I have to restart my PC.
Here is another instance I found, exactly the same phenomena as I encountered.
Kingston Predator SSD only performing at half speed!?
As a comparison, when using the drive on another system (i7-4790 + ASRock Z97 Extreme 6, drive installed on PCIe slots to CPU or Ultra M.2 port, running at Gen2x4)
Perfomance of random 4KB QD32 T1 exceeds 110K IOPS for both read / write, and there is no problem with more threads (at least running well with QD32 T8)
(2) AHCI driver for PCIe SSD?
The AHCI driver I downloaded here (Intel RST 11.2) works perfect for my SATA SSD/HDDs, however, not for PCIe SSD.
When running AS SSD Benchmark, it shows msahci, not iaStor.
Am I able to use Intel RST on the PCIe SSD? Or it’s a hardware limitation?
On the below are screenshots from device manager, it seems the PCIe SSD is not controlled by Intel AHCI controller.
The model name is attached with “ATA Device”, under controlled by "Standard AHCI 1.0 Serial ATA Controller"
Thanks for reading the post. 
@Houting :
Welcome at Win-RAID Forum!
My short answer to your question: Only the MS in-box AHCI driver supports M.2/PCIe connected SSDs, which are using the AHCI protocol.
Regards
Dieter (alias Fernando)
On the below is an additional benchmark between Win7 & Win8.1 with the same drive on PCIE5 of Z97 Extreme6 (runs at Gen2x2)
It seems performance drop is due to msahci of Win7, as well as the “system freezes” phenomenon previously mentioned.
Really big difference on performance of random 4KB QD32.
@Houting :
The tool CrystalDiskMark is not the best, if you want to compare the performance of 2 different SSDs or the performance of a certain SSD under different conditions (driver version, SATA/PCIe port etc.).
I recommend to take Anvil’s Utilities instead.