No, CGI just optimises the DMI bus for handling lots of highspeed peer-peer writes between the PCI-E 16x and 4x slots. The Blitz literally splits the 16x slot into two 8x slots which has two advantages - more bandwidth for the second card, peer-peer writes can (presumably) happen directly in the crosslinx IC.
There shouldn't be much of a boost in most games, however the ones that gain no performance boost in 16/4 should get one now (a big one). Try COD2, that only likes 8/8 and above.

