RAID0 on MSI P6N Platinum

[two bit hit]

I bought two new 500GB Seagate Barracuda 7200.11 and in RAID0 I'm only getting ~150MB/s, when I was expecting 250MB/s seeing as though I've seen 250 achieved with lesser drives in RAID0, does anyone know why this could be? The only thing that I can think of is my chipset, hence the title. I can't find the update of the drivers for my board for 64bit Vista.

The motherboard is an MSI P6N Platinum SLI, with a 680i chipset.

Any ideas?

 

[two bit hit]

It's a 650i, sorry and the SB is a 430i, which is more relevant I suppose for RAID.