It's not a good idea to not do journalling for an external drive. No matter how careful you are, it is just a matter of when you will trip up your USB cable in the middle of a write; and then you should just pray that fsck can save your drive without the journal.

Also, it probably won't hurt using ext4, given that ext4 had several performance improvements over ext3. However, as Theodore T'so - the primary developer of ext4 - said, ext4 is a stopgap until btrfs is ready. IMO, from my experience of using btrfs some time ago, I'd say that btrfs is pretty much ready nowadays.