No. Stratix® IV GX devices do not support PCIe Gen 2 x1/x4/x8 in C4 and I4 speed grades. Stratix IV GX devices with speed grades C2/C2x/C3/I3 should be used to support PCIe Gen2 x1/x4/x8.
Quartus® II 9.1 and earlier versions may compile the PCIe Gen2 x1/x4/x8 in C4 and I4 speed grades. This is a software bug and will be fixed in future Quartus II release.