FWIW, I have CX90s running with 6700 levers and they're fine albeit slightly binary. I think the CX84 were put out specifically to play nice with SRAM/Campag (CX90 had too much mechanical advantage for them) as well as tone things down a bit for the Shimano crowd. Plus added rim clearance.
Ah right, I forgot Shimano keep changing their cable pull. Good info