Actually it was implemented in the 4870 X2 and 4850 X2 but never used. By eliminating they mean they did not implement it at all in the 5970.
Originally Posted by rico2001
"Eliminates" is a strong word, more like choosing not to enable the feature. It would not boost performance, it would prevent any bottlenecking of the pci-e bandwidth throughput. Sideport still not needed and I imagine may never be enabled since pci-e 3.0 is in the near future. But who knows... Ati may be saving the sideport for some triple gpu card down the road.