From Stratix® III, Stratix IV and Arria® II GX devices onwards, Altera® uses system-level specifications such as external memory interface specifications as an indication of I/O buffer performance. Actual achievable I/O signaling frequencies depends on design and system specific factors and is best determined using HSPICE / IBIS simulations. Altera will discontinue publishing the I/O toggle rate specifications in the device data sheets.
In addition, selected families such as Arria II GX devices will have absolute maximum allowed I/O operating frequency specifications to ensure device reliability.