Choosing Interconnects for Grid Databases?

cybrthng asks: "With all of the choices from Gig-E, 10 Gig-E, SCI/Infiniband and other connections for grid database applications, which one is actually worth the money and which ones are overkill or under performing? In a Real Application Cluster (RAC), latency can be an issue with cached memory and latches going over the interconnect. I don't want to recommend an architecture that doesn't achieve desired results, but on the flipside, I don't necessarily want overkill. Sun had recommended SCI, Oracle has said Gig-E and other vendors have said 10 Gig-E. Seems sales commissions drive many of what people recommend, so I'm interested in any real world experience you may have. Obviously, Gig-E is more affordable from a hardware perspective but does this come at a cost of application availability and performance to the end users? What has been your success or failures of grid interconnects?"