The 3Gb interface really isn't the limiting factor, most drives are INTERNALLY limited to about 60MB/sec transfer rates due to head seeks, etc. 10k and 15k rpm are faster but still max out at around 125MB/s

Since the interface can handle 3Gb, each time you add a hard drive, you increase the transfer rates. Think of it this way, the sewage pipe leaving your house might be 6inches in diameter (the interface) but the drains from your sink, tub, toilet, (HDD's) etc are only 2inches in diameter. No matter how many times you flush the toilet, you'll never fill the main sewage pipe leaving your house. Flush the toilet, and run every faucet you have, and you might!

Of course, whether the CPU/GPU can crunch all of the data from all of the HDD's at the same time is a whole 'nother story.

*I can not be held responsible for any damage that may occur from the flushing of toilets, running of faucets, or the costs attached thereto.