I have the above pieces of hardware with an Intel i5 3570k CPU. When I run benchmarks, I see sub 400 MB/s R/W. When I disabled AsMedia (as per this link http://www.tomshardware.com/answers/id-1651734/ssd-inte...) in the BIOS I lost my Sata III A0 and A1, but my DVD burner remained connected on Sata III 1. I'm not sure what the difference is between A1 and 1, but according to my BIOS and manual, I am connected to the Sata III ports. Hopefully the pictures answer any additional questions about where the SSD is connected and my firmware version, etc.
Full system internal list:
OS Windows 8 x64
CPU Intel i5 3570k Quad Core 3.4GHz
Motherboard ASRock Z77 Extreme 4
Memory Crucial Ballistix Sport 8GB DDR3 1600
Graphics Card Nvidia GeForce GTX 550TI w/GTS 250 as PhysX
Sound Card Sound Blaster Z
Samsung 840 Pro 256GB SataIII SSD
More about :samsung 840 pro speed issues asrock z77 extreme4
I figured out my problem. Apparently, the Sata III ports on the AsRock Z77 Extreme 4 motherboard are different. Once I switched my SSD from the A1 port over to the 1 port (Yes, without the 'A') my benchmarks went through the roof. However, moving over to this port caused my machine to reboot repeatedly after exiting BIOS. I ended up having to reinstall the OS and format the drive. Now lookie:
Still doesn't seem to be as good as I've seen from others who have a similar setup. I wonder if additional tweaking is in order.
Edit: Here's a Samsumg Magician benchmark I just ran: