The expected device speedgrades required to support PCIe® in SOPC Builder are expected to be very similar to Cyclone® III speedgrades for the Avalon®-MM Interface types.
The current PCIe UG is actually missing key information regarding C4GX HIP speed-grade support for the Avalon-MM interface.
1) For C4GX in SOPC Builder PCIe x1 @62.5Mhz, all speed-grades are supported (-6,-7,-8).
2) For C4GX in SOPC Builder PCIe x4, x2 or even x1 @125Mhz, the speed-grade value should be: -6 (or the fastest speed grade) due to fabric performance.
These numbers are preliminary pending device characterisation.