I'm using iMac 27" late 2012. I have 1 TB HDD, and I want to boot Yosemite through an external SSD drive. I was thinking about Samsung 850 evo with segate goflex thunderbolt adapter (allowing me to use TRIM and to boot with it). The question is, how fast is it going to be? Obviously not as fast as an internal SSD, but opening the imac is a big hassle and I'm still under extended apple care warranty. Are there any benchmarks comparing these two? It's about 250$ upgrade and I want to be sure it's worth it. If you have other suggestions for HDD or thunderbolt adapters I'll be happy to hear (I guess the thunderbolt cable shouldn't be something special, right?) Thanks!