I've used a Little Big 2 TB for several months and I'm very happy. I have a couple of WD black drives, but not configured with a USB 3 enclosure you mentioned. This review is about a LaCie Little Big 2 TB. I can tell you after conducing speed tests while the drive was fairly new and with real world experience the following:
1. The drive speed ranges from write 95, read 189 for a 128k file and up to write 191, read 195 for a 16 GB file. All in MB/s with the drive configured in Raid 0. Honestly, I use the drive to transfer several files with their total approaching 5 GB.
2. I didn't conduct speed tests in Raid 1 in which the drives would be slower, as you know. Also, the drive in question can be hot swapped, but LaCie doesn't recommend it. Also, the hdds are the 2.5" variety just in case you didn't know. So if you are a 3.5" drive fanatic, need not apply.
3. Transferring from Thunderbolt to Thunderbolt is much faster than transferring from my MBP to Thunderbolt. Expect a Thunderbolt to Thunderbolt speed increase of at least 20%. I don't have a SSD in my MBP, so obviously my hdd is the bottle neck vs. two hdds of the Thunderbolt drives. It's still plenty fast for what I use it for, which is photography!
4. Thunderbolt externals begin to slowdown when they exceed 50% of their capacity. I will conduct speed tests with my drive as it has 750 GB of free space. I suppose this happens with all hdds though.
5. The price has dropped significantly since I bought my Thunderbolt external earlier this year. I think B&H Photo has the a 2 TB Little Big for $450 or so. Happy Shopping!
6. LaCie introduced new SSD externals and they are supposedly much faster than their previous offer. FYI and in case you want max speed!
Conclusion: I would buy a Little Big again even for the price I paid as the file transfer rates are worth the extra coin. You can wait a few more months and the prices most likely will decrease or you start using Thunderbolt immediately!
Oh yeah, you need a Thunderbolt cable for each drive just in case you didn't know. Another note, I have a three device daisy chain, which includes two Thunderbolt externals, a NEC monitor and my cpu temps spike up to 128f degrees constantly. I talked to a Genius in my local Apple store and he said it's normal and there are some heat problems with Thunderbolt daisy chains. He didn't go into detail because I didn't ask. I hope this write up helps you in more ways than one!
EDIT: I took screen shots of each file size, so if you want a speed for a particular file size, just ask.
