It's possible that the throughput of a low-end GPU will be much less affected by Thunderbolt's latency and 4-lane limit, but that kind of defeats the purpose of getting an eGPU in the first place.

When Intel and Apple released Thunderbolt, hallelujahs from the Apple choir were heard. Since very little in any of Apple’s hardware lineup is upgradeable, an external video card is the best of ...