In most cases I would consider it a bit too reckless. When a disk does go bad in an array with such large disks, your rebuild time will be very long - about an entire day in fact. If another disk takes a dive during the rebuild window, or even if you have unrecoverable errors on just part of the disk during that time, then you are looking at a failed array requiring a full restore from backup. And since disks tend to fail in clumps as opposed to randomly, the odds are higher than you'd expect. ZFS will be a bit less likely to fail and faster to rebuild than hardware RAID5 I am told, especially if you have much less data than you do capacity, but the general problem is the same.
Personally, I can remember having to do about 10-15 RAID5 rebuilds due to disk failures in my lifetime - I am an accidental sysadmin so this number of quite low. Twice I've had a second disk go bad during the rebuild. Perhaps my luck has been much worse than the average, but my experience has certainly soured me on RAID5.