You only included a v5.0.5 syslog, so cannot tell anything about how well v6.0-beta4 booted. There appears to be a good shutdown from v5.0.5, so there should not have been any problems on the subsequent boot. There is however a small oddity in this v5 syslog, with the 2 following lines (probably not important, but worth mentioning):
There are no clues as to what write was attempted, and no clue as to where. I suppose it's possible this was a write to the super.dat file on the flash drive, which could potentially cause a parity check, but no proof here at all, and seems very unlikely.
Good point on the start up log, I should have known better. Of course, I do not have it because I didn't think to save it and haven't gotten powerdown up and running yet on 6b4, so that's not good... Best I could do is revert to my 5.05 backup and test to see if I can make the same behaviour occur again. Might try it later this week if I have time as I'm on the road till Wednesday at least.
Thanks for the help!