high-end gaming doesn't demand as much from the hard drive as people seem to think unless you don't have enough memory.
Again, the speed of the PCI bus is faster then any HD is capable of delivering data; that is, the PCI bus runs at 133Mhz, and in many cases transfers twice per clock cycle, giving an effective rate of 266Mhz, either way, you won't be trying to transfer anything more then a few megabytes from any one hard drive at a time, regardless of the programs you run.