The more I thought about this last night the more I was comfortable with splitting up my array to not be consistent. If I lose a drive, especially a parity, I hope its on a different schedule than my other drives.
I am also curious how sensitive is the parity "largest drive" requirement? I haven't shucked the Seagate yet so I don't know if it is 100% of the same size as the other 8TB drives. Is the requirement down to the byte or does unRAID give some leaway as long as they are very close? If I lose a few MB of storage so that the array works I'm fine with that. I'd rather answer my own question than asking here but I'm still in the first of three passes on pre-clear, almost 30h in, and I still need to do the Seagate before I'll be able to find out from the unRAID setup.