Well, that upgrade was way easier than I expected. I didn't think WinXP would like being moved to different drives on a different controller. But it worked perfectly. Installed the TX2000 and the hard drives, configured the array before booting into Windows using the original boot drive. Installed drivers (important to do that before trying to swap). Benchmarked, scored twice as high (40k to 42k; didn't record details) in Sandra as my Barracuda ATA IV (tried with dynamic disk and basic disk, no statistical difference). Didn't get quite so good a leap in HDTach, but that isn't a worry to me since HDTach has all sorts of issues. Burst throughput was off the graph (HDTach still won't show me more than 80MBps), sustained sequential read averaged 45MBps. I can't remember what my 'cuda scored before, but I seem to recall it being in the 30s.
After testing, ran Ghost, which didn't like the TX2000 when setting up the copy in Windows and letting it reboot with its "virtual partition" to run PC-DOS. I finally just made a boot floppy (copied to bootable CD) using MSDOS from a Win98SE disk. Despite loading no drivers of any kind, MSDOS was able to read the RAID array perfectly well. Maybe PCDOS just doesn't have the functions built in that allow it to read an external controller. Ghost copied the old drive to the array. Unplugged the old drive, booted to the RAID array with absolutely no complaints from XP. All closed up and running now. Getting Ghost to run was the hardest part of the process, and the longest.
The system definitely feels snappier, and boots pretty well faster. I'm using a 32k stripe size, just chose that after using a disk usage tool and seeing what file sizes were common. I'm quite happy with this upgrade, not TOO expensive (total of 230 bucks) and it helps make the system seem more responsive and less like I have to wait for it. Maybe one day software makers and driver writers and hardware makers will learn to coordinate and make use of all the system power so that the user can stop getting the feeling like he's waiting for the system to work when in fact there's just always one item making all the other parts idle.