I've been curious about developments in this area for a couple weeks now, but information seems sketchy at best. Here's what I've come to understand:
- Some folks have them working via Thunderbolt PCI-E adapters under Windows.
- Those who have used some high end options say that the GPU suffers around a 3-5% performance decrease over Thunderbolt (which I'd say is acceptable for an external solution).
- Currently there are no Thunderbolt aware GPU drivers for supported GPUs on Macs.