The resulting 150 MB/s is not a limit set by the controller; rather, according to Adaptec, it has to do with the NTFS file system. In fact, we got higher data rates with IOMeter - for details see the IOMeter results.
SCSI: LSI MegaRAID 320-2
The LSI controller as well showed a hardly satisfactory performance with Winbench 99 2.0. Here, too, IOMeter delivers the better and more reliable results (see below).