Yes, I think you are confusing units here. MB (capital B) is groups of eight bits, as in mb (lower case).
So, 330 mbps is a bit more than 40 MBps, which even a single SATa drive can deliver today. Any RAID should deliver more than that, and I suppose yours is doing 300 MB per second.
The problem must be somewhere else.
Director of the Institute of Media Research (IMF) at Braunschweig University of Arts