Actually the total amount of space is well under 1 TB. There are 2 x 300 GB in a RAID 0, plus 4 X 73 GB in a RAID 5, for a total of 600 + 200 = 800 GB. After switching to a completely different card, things are just fine.

As for performance, I'm not sure HDTune is such a good benchmark for this stuff (its main advantage, though, is that it's free and relatively fast, and reproducible). In addition to those numbers, I spent a bit more time copying my own data files.

I had a set of digital video files, each about 2 GB, for a total of about 14 GB. Copying to the RAID 0 gave an average of about 53 MB/sec; to the RAID 5, about 45 MB/sec. This is a lot more reasonable. Over the long run, with a big mix of files (160 GB total) of all sizes, I get about 19 MB/sec with the RAID 5, which is reasonable since there are a bunch of smaller files.

This seems a bit better overall, and suggests that there isn't anything seriously wrong with the setup. I'm a bit interested in others' real-world experiences, though. Is there much more performance to be had? Right now, I'm using the integrated ethernet cards on the workstation motherboards on a dedicated switch---should I expect a significant increase by going to dedicated, plug-in server ethernet cards? Will jumbo frames make a big difference? Doesn't look like I'm very close to saturating the Gig-E connection, but should I be considering dual-port cards? Thanks!