OS on external SSD for performance? I have a 2011 iMac 27", and back then opted for a HDD. Back then (and now still) I fear for the lifespan of SSDs, and hauling an iMac 27" to the store is cumbersome, so it looked the right choice.

But now, I notice that the drive is the main bottleneck for pretty much anything I try to do, and I would love to benefit from the better performance of an SSD. (Though still not regretting my choice for HDD internal storage, mind.)

Will installing OS X and my applications on an external SSD be faster than an internal HDD?

If I did my reading right, I really should be getting something with a Thunderbolt connection. But I wanted to check here to be sure, and wondered if OS X is at all bootable from a Thunderbolt drive?
To answer your first question, Yes booting from an external SSD should be much faster than a stock HD.

Thunderbolt is definitely the fastest interface around so that shouldn't be the bottle neck.

Yes, from a brief Google search it looks like people are booting from  Thunderbolt drives without a problem.