I'm marking this thread solved.
I've tested ext4 with settings of: journal_data, journal_data_writeback, and journal_ordered.
I've increased commit="seconds" to 30, 60, 90, 120
I've tried "noatime" parameter.
And several different mixtures of all three above.
I'm getting the same performance on this hardware: 70MB/s. Read & 24-25MB/s. Write.
I'm speculating, but I'll posit the largest factor affecting performance is the older SATA 1 onboard controller working with Raid1. The cpu(s) are 2 dual-core opterons running at 2.2Ghz with 4 gigs. of ECC RAM, so I don't think there's a performance problem there. When I tested single hard-drive performance on the WD 500Gig. ABYS drives, I was getting 50 MB/s. Writes and 75-85 MB/s. Reads.