Sorry to resurrect an old thread, but some current threads are pointing to it and this information is relative.
I did some experimenting over the weekend with a portable Thunderbolt GoFlex, USB-3 GoFlex, and a Thunderbolt "LaCie LittleBigDisk" RAID-0 2.5" hard disk ... all running from a 2012 Macbook Air (only Mac I have with a USB-3 port).
I used 2 different GoFlex hard disks, one normal and one Pro, and a Crucial M4 512GB SSD. These Seagate GoFlex TB and USB-3 interfaces are pretty cool since you can simply plug in any standard 2.5" SATA device to test, and you can purchase empty shells on eBay if you want to make it more permanent. They also have a FireWire 800 interface cable available.
There was no benefit in speed between the Thunderbolt and USB-3 interface when using either hard disk. The speed was disk I/O limited.
There was noticeable benefit in speed with the SSD when using the Thunderbolt interface.
The advantage of the Thunderbolt interface to me with hard disks is that all of my Mac computers have a Thunderbolt interface on them, but only 1 has a USB-3 port at this time.
The LaCie performed well with the RAID-0 hard disks ... but my intention is to remove the hard disks and put dual SSD drives in the Thunderbolt enclosure to use with my new iMac.
Here are some numbers:
Wr/Rd MB/s -- interface -- drive type
-------------
45 / 49 -- USB3 -- slow hard disk (5400 rpm ??)
43 / 49 -- TB -- slow hard disk
84 / 82 -- USB3 -- fast hard disk (7200 rpm ??)
83 / 82 -- TB -- fast hard disk
167 / 194 -- USB3 -- SSD
260 / 382 -- TB -- SSD
148 / 154 -- TB -- LaCie RAID-0 hard disk
? / ? -- TB -- LaCie RAID-0 SSD
The Crucial M4 SSD has 260 / 506 MB/s when on a SATA-III PCIe card in my Mac Pro. I have not tried them as Raid-0, but a pair of OWC SATA-II SSD in RAID-0 show 306 / 311 MB/s on the Mac Pro SATA-II ports.
All measurements were made with BlackMagicDesign "Disk Speed Test"
(This table will probably lose all formatting when I post it ... sorry)
-howard