Thanks to both of you for the input.
I'm thinking of grabbing the WD Thunderbolt 6 or 8TB drive.- along with at least one extra 3 or 4TB drive to use as backup. I'd run the two drives in the enclosure as RAID 1 or perform my own back ups using ChronoSync while they are set to JBOD.
Initially it's more expensive but seems easy enough to swap drives. My only concern is that the 6TB model only runs 5400 rpm drives but the new 8TB runs 7200 rpm 4TB drives. I guess I'll have to do more research to find out if the newer model has a fan to accommodate the exrta heat from the 7200s.
I like how the ICY Dock has a fan though...does anybody notice a big difference in 5400 vs. 7200?