So then with this PLX chip: http://www.plxtech.com/products/expresslane/pex8648.asp
48 Lanes can be divied up into 16 for link to main board, and 16 to each GPU... from the spec page, it seems it can allow for a flow through (non-blocking) passing of data in both host centric, and peer to peer... Allowing I guess for system to pass same data to both cards at once without having to share the 16 lanes between two gpus... further it then allows full 16x PCIE 2.0 comm between GPUs... So from PCI SIG FAQ, that's about 16GB/s... Add to this whatever bandwidth is available through Crossfire Side Port... and that's not bad... Certainly greater then whats available on the 3870x2.

Is it enough to then to start using the other gpu's memory / cache to make 2 gpus and 2 sets of memory better then the sum of its parts?