As per the 3rd graph, the reads peak out at almost 350MBps, so I think your set up os right. Your BIOS must be set to RAID, and 128K stripe size in spot on.
Run the 1st graph again, and see if you get an average over 300MBps, will a max close to 400MBps. That's what mine do.
IMHO: The 1TB will be faster (or close) than 2x320GB in RAID 0, due to data compression and platter size of the Black.
My 1TB Seagate 7200.12 1TB is almost as fast as my 2x500GB Seagate 7200.11 in RAID 0.
I posted my benchmarks in here, let me find them...couldn't find 'em, so here they are:
SSD benchmark: 2xIntel X25-V 40GB in RAID 0 -
HDD in RAID 0 benchmark: 2xSeagate 7200.11 500GB in RAID 0
HDD non-RAID: Seagate 7200.12 1TB