External graphics card via thunderbolt to speed up transcoding with davinci resolve

hello together,
I was wondering if I can run an external graphics card (PCI) from nvidia in a external pci housing via thunderbolt with my macbook pro 17 inch, 2.4 GHZ (the last one built).
I would like to speed up my transcoding and as far as i know the graphic cards which is accelerated by cuda is the crucial part. I also have a internal additional SSD drive where i run my OS from. I have a AMD radeon HD 6770M graphics card as the Open CL one which is not ideal i know because it is not nvidia.
Somehow my transcoding speed are not constant. I was once on 40-45 fps where now I am hanging with 12-14.5 fps what is a massive difference and I havent changed anything hardware wise. Any Idea what that could be?
Please give me advise how I can get my proper transcoding speeds again.

It is not yet possible to use an external graphics card, at least not affordably nor without having to boot into Windows, but with Thunderbolt-aware drivers which would also allow hot-plugging, it may one day be possible. In fact Village Tronic and Silverstone are each working on affordable eGPU enclosures, which I hope they’ll be able to begin selling this year, especially since they’ve been working on them for a year or so and many people(myself included) really want an affordable eGPU enclosure.