I just installed Windows 7 Ultimate 64-bit to a new Samsung 850 Pro 256 GB SSD on a system with an Asus Sabertooth P67 motherboard and 16 GB of RAM. The drive is plugged into a 6 Gbps Intel port and the UEFI is set to AHCI for the Intel SATA ports. Windows is up to date and the Intel drivers are all the latest drivers that I can find, although the SATA AHCI Controller driver is version 10.5.0.1026 from 4/26/2011 as it was downloaded from Asus and I could not find a more recent driver from Intel.
I could live with the sequential speeds, but the IOPS are just pathetic compared the drive's capability. I do have TrueCrypt 7.1a with full disk encryption, but given that the system has hardware AES, TrueCrypt reports throughput benchmark of 3.4 Gbps, so I'm not clear that this would affect anything.