My new memory is flawless. I ran Apple Hardware Test on it (passed), then I rebooted into single user mode and ran Memtest five times (the recommended maximum), and it found no errors whatsoever. Even though Memtest took about three hours to run, the time away from the computer was worth it. I know that I have quality RAM in my system.
Unfortunately, no one is online to share my joy. I’m going to go play with GarageBand. OOH! I bet I can totally work with the “Only” remix now!
(UPDATE: it works perfectly! Me and Kelly are going to make a million “Only” remixes)