Definitely getting more random reboots on 6.4a than I did on 6.2a (which were virtually zero). No freezing or stuttering issues, just random reboots. I have 4 units that used to be running 6.2a, the 3 "upgraded" to 6.4a exhibit this new behavior. It's not excessive, but it is a noticeable change. It's not the drives, let's get that out of the way right now. 1 has a new drive and 2 others have the same as the drives that had 6.2a, all check out good with SpinRite.
Unit kept at 6.2a is rock solid. It will play a music channel for days on end without an issue. (Maybe it's rebooting always at night?... I listen to music way too often to never catch it.) 6.4a unit did it to me yesterday and again on Friday.
Nothing scientific here, but I've lived with these 4 units for a while now and I'm very familiar with how they act and perform.
Just wanted to post my experiences so perhaps other people won't think they're crazy (crazier?).
And I do know it's time to upgrade hardware. But these units (used to... and mostly still do) work so great for certain applications, like bedroom and garage CRTs. If it weren't for the local channels and guide data thing...