This is a known problem on the 680i platform to crap out at ~120mbs. There is an article on it in Anandtech.
Ther workaround is to deselect the write caching and command queuing for both channels of the raid controller in the device manager.
The good news is even if you buy a $350 hardware raid controller you probably won't see a significant real world difference...so I'm told. I have a few friends who did just that and there rates went up to ~160mbs which is about the limit for the 150g raps and probably is meaningless for applications because there are other parameters that affect hd performance. Just for fun I've just ordered a $35 job to see if there is any change.
EDIT: Well I got a better speed.. 111.7MB/s hahaha... and 136.2 MB/s on the faster one... I think that's a record...
every little bit helps though thanks... Rep+
http://www.overclock.net/hard-drives...single-10.html <( I think it is the current 7200rpm OCN RAID0 record!!!)
brought it home from the stupid Intel South Bridge.. hahahah muahahahah...
About the point you make about buying a RAID controller... I bought the "best" controller for under $120 and it was crap... then to get a good one with a processor and big cache it is about $300 to $500 and they will do the same or worse.... very good point... that was actually the reason why I bought this board... otherwise I would have stayed with a cheaper MoBo... this South Bridge saved me money