The IDT74SSTU32864C zip file contains IBIS models with output load treated 
just as a discrete RC load and as a transmission line plus discrete RC load. 

When treated as a transmission line plus discrete RC load, the
output model was created with the output load treated as part of the output
circuit with nominal 10 Gig load treated as an external load. 

The IBIS files are as follows

Discrete RC Load
----------------
4pw864cy_2n.ibs

Transmission line plus Discrete RC Load
---------------------------------------
4pw864cy_2t.ibs
