I do have one question about hardware errors and power (I have actually read this entire thread several times grasping at anything). I am getting maybe one hardware error (on each stick) every two hours (frequency doesn't seem to matter - about the same rate at 75 MHz as 150 MHz). Is that "good enough," or should I try to up the voltage?
Once every few hour should fall into the not noticeable category.
You would want to keep an eye on WU (Work Utility).
If it is very close to 1.53 x frequency then the HW errors are negligible (~150 default settings).
https://bitcointalk.org/index.php?topic=1764803.msg18329715#msg18329715