Hi - as you can see in your results the xdisk tool with 1 MB block size drove the V7000 up to 3.4 Gigabytes per second.
The reason I mentioned using 0x40000 for the hdisk max_transfer is because...
Can you change the hdisk max_transfer size from 0x80000 to 0x40000 and re-test? You will have to unmount the filesystem, varyoff the VG and run the chdev command.