Ok, the two 72GB drives are set up RAID1, and the four 146GB drives are set up striped, RAID0. The two 72's are on channel 1, and the four 146's are on channel 2. Under CentOS 4 with the hardware RAID running, the four 146's (hardware RAID0) have a raw read performance of abut 150MB/s, which I thought was pretty good.
Now, the box has dual 3GHz Xeons (it needs them for the pulsar dedispersion algorithm's FFT's, particularly when we refine it to do dedispersion in real-time). With FC5 installed, and the four 146's running software RAID0, I am getting nearly 240MB/s throughput (with other processes running). The box feels significantly more responsive; the GNUradio build with the PERC running in hardware RAID mode took about thirty minutes; with it running in LSI MPT SCSI mode it's taking half that time to build and install.
Just thought I drop this data point in.
/me wonders whether that Dell RAID system was using Intel i960 cpus :P