Seagate Barracuda XT 2TB: SATA 6Gb/s Performance Preview
 

See something strange, the read burst rate of 2766MB/s and write burst of 2705MB/s are incredible for single drive performance but like most synthetic test results, they are not a true indication of actual platform performance. The reason for these “outstanding” results is that Marvell’s latest driver allocates (dynamically) a portion of system memory for transfer cache operations. Intel’s own Matrix Storage Manager and JMicron’s latest driver set also utilize a similar approach. In fact, Windows 7 implements a similar type of caching at the kernel level that makes these driver optimizations redundant in some ways.


The Marvell controller is 19% slower than the Intel controller with the WD drive and 18% with the Seagate drive. The WD drive is up to 28% faster than the Seagate drive.

http://www.anandtech.com/storage/showdoc.aspx?i=3668

since when do single HDDs require more than SATA 300 ?