Okay, I give up for now — it's been 7-days (without a single crash/reboot) as of today, and just when I was about to feel like I'd solved it, it crashed after being asleep for 40min, mid-day... not even an overnight sleep session. I'm in agreement with
@wagonfixin that this is a firmware issue (not software / not a PSU & MLB failure) but I'm not 100% sure that it's impacting EVERY 6,1 MP user either — I feel like I'd see more of the exact same convo on the apple support site if it was a completely unanimous issue. So, I'm not sure if they're seeing/hearing issues from enough people to make it a priority fix in the next FW rev. Also... who knows when there might even be another firmware update?! So, I'm gonna just deal with it for now... it certainly puts any of us in an annoying position for reselling these machines if/when we move off of them. I don't wanna not-disclose an issue, but I'm convinced it's NOT a hardware issue.