I have a 27" 2011 iMac with a 1TB internal hdd. And although it is actually fast enough for all what I do with it, I am thinking about adding an external ssd on the thunderbolt port and use it as a boot-drive.

SSD drives are expensive, but the LaCie 256GB SSD Rugged Thunderbolt/USB 3.0 Solid-State Drive is beginning to get from the 'way too expensive' range into the 'expensive' range. I've seen good reviews of the 512 GB SSD Little Big Disks, but these are twice as expensive as the Rugged.

I intend to use the disk only as a boot disk. Anyone any idea about what the performance difference might be between the 'Rugged' and the 'Little Big'?