I have seen higher values in the sequential / 512k department, but only slightly. One guy posted a screenshot with a sequential result just over 500MB/s for a RAID-0 setup like yours for instance. But this might just be because of controller / platform differences, so I suppose your result should be pretty good and in line with what is usually being achieved.
These were my results on a DFI - P45 ICH10.
Since I've experienced that one ssd becomes disconnected after a while (System freeze) and gets set as failed during Post I've been in touch with the Intel Hotline.
The help was not really what I expected, but now they are aware. I've RMA'ed the (twice) failed drive.
I hope that you do not have the same problem with your setup.
What chipset (Board) and OS u use?