Regarding the performance, I have some notes for your reference.
1) Bobby used the GTX 660 on his MacBook Pro9,2with the Sonnet Thunderbolt to ExpressCard Adapter and had the following Benchmark results: (Frame rate MacBook) {Framerate MacBook with ViDock & GTX 660} [percent performance increase]
Battlefield 3: (4) {46} [1050%]
Far Cry 3: (10) {58} [480%]
Just Cause 2: (6) {46} [ 666%]
Arma II: (5) {46} [820%]
Minecraft: (46) {82} [178%]
2) Sony Vaio VPC-Z12V9R/B + GTX 670 + ViDock 4 Plus Overdrive
3dMark Vantage with Asus GTX 670 is ~20k in comparison with ~5k with the standard GT330M card http://www.3dmark.com/3dmv/4507623