Let me clarify, a high end gpu will be 64gb/s, plugging it in a thunderbolt makes it only be able to run at 10gb/s, thus a bottleneck. Even a lower card, lets just say 32Gb/s in a 10Gb/s, still a bottleneck.
Now current solutions, people are using what is available to them. Here are some linkshttp://www.villageinstruments.com/tiki-index.php?page=ViDockhttp://forum.notebookreview.com/gaming-software-graphics-cards/418851-diy-vidock-experiences.html#post5324240
As I said before, its still an improvement over the ipgu and worth doing if you really want to. Just know that you are only using a fraction of the cards actual power.