HyperOS claims an 1,100 ns read seek time and 250 nm write seek time. The total access time, measured by c't magazine's h2benchw benchmark, was 0.04 ms. In any case, access time can be considered effectively eliminated here. The SanDisk Flash SSD5000 takes roughly twice as long to access read data.
These results really are impressive: Using the Areca ARC1280ML controller with its cache memory, the total bandwidth is 562 MB/s for a single HyperDrive 4 and 603 MB/s for a RAID 0 that consists of two HyperDrive 4s. A WD Raptor WD1500 seems to outperform a single HyperDrive 4, but this is only because the interface bandwidth test reads directly out of the hard drive's cache memory, which of course saturates the SATA/150's bandwidth. The interface bandwidth of the HyperDrive 4 actually represents its sequential throughput.